Move blame buffer settings to FileType event

The goal here is to extract just the settings that would work outside of
a vertical split with 'scrollbind' in effect, so we can one day add a
second mode.

autoload/fugitive.vim

@@ -4553,17 +4553,6 @@ function! s:Keywordprg() abort
   endif
 endfunction
 
-augroup fugitive_blame
-  autocmd!
-  autocmd FileType fugitiveblame setlocal nomodeline | if len(s:Dir()) | let &l:keywordprg = s:Keywordprg() | endif
-  autocmd User Fugitive
-        \ if get(b:, 'fugitive_type') =~# '^\%(file\|blob\)$' || s:BlameBufnr() > 0 || filereadable(@%) |
-        \   exe "command! -buffer -bar -bang -range=-1 -nargs=* -complete=customlist,s:BlameComplete Gblame :execute s:BlameCommand(<line1>,<line2>,+'<range>',<count>,<bang>0,'<mods>',<q-reg>,<q-args>,[<f-args>])" |
-        \ endif
-  autocmd ColorScheme,GUIEnter * call s:RehighlightBlame()
-  autocmd BufWinLeave * execute getwinvar(+bufwinnr(+expand('<abuf>')), 'fugitive_leave')
-augroup END
-
 function! s:linechars(pattern) abort
   let chars = strlen(s:gsub(matchstr(getline('.'), a:pattern), '.', '.'))
   if exists('*synconcealed') && &conceallevel > 1
@@ -4745,27 +4734,10 @@ function! s:BlameCommand(line1, line2, range, count, bang, mods, reg, arg, args)
           setlocal cursorbind
         endif
         setlocal nonumber scrollbind nowrap foldcolumn=0 nofoldenable winfixwidth
-        if exists('+concealcursor')
-          setlocal concealcursor=nc conceallevel=2
-        endif
         if exists('+relativenumber')
           setlocal norelativenumber
         endif
         execute "vertical resize ".(s:linechars('.\{-\}\ze\s\+\d\+)')+1)
-        nnoremap <buffer> <silent> <F1> :help fugitive-:Gblame<CR>
-        nnoremap <buffer> <silent> g?   :help fugitive-:Gblame<CR>
-        if mapcheck('q', 'n') =~# '^$\|bdelete'
-          nnoremap <buffer> <silent> q    :exe <SID>BlameQuit()<Bar>echohl WarningMsg<Bar>echo ":Gblame q is deprecated in favor of gq"<Bar>echohl NONE<CR>
-        endif
-        exe 'nnoremap <buffer> <silent>' s:nowait "gq :exe <SID>BlameQuit()<CR>"
-        nnoremap <buffer> <silent> <CR> :<C-U>exe <SID>BlameCommit("exe <SID>BlameLeave()<Bar>edit")<CR>
-        nnoremap <buffer> <silent> -    :<C-U>exe <SID>BlameJump('')<CR>
-        nnoremap <buffer> <silent> P    :<C-U>exe <SID>BlameJump('^'.v:count1)<CR>
-        nnoremap <buffer> <silent> ~    :<C-U>exe <SID>BlameJump('~'.v:count1)<CR>
-        nnoremap <buffer> <silent> i    :<C-U>exe <SID>BlameCommit("exe <SID>BlameLeave()<Bar>edit")<CR>
-        nnoremap <buffer> <silent> o    :<C-U>exe <SID>BlameCommit("split")<CR>
-        nnoremap <buffer> <silent> O    :<C-U>exe <SID>BlameCommit("tabedit")<CR>
-        nnoremap <buffer> <silent> p    :<C-U>exe <SID>BlameCommit("pedit")<CR>
         nnoremap <buffer> <silent> A    :<C-u>exe "vertical resize ".(<SID>linechars('.\{-\}\ze [0-9:/+-][0-9:/+ -]* \d\+)')+1+v:count)<CR>
         nnoremap <buffer> <silent> C    :<C-u>exe "vertical resize ".(<SID>linechars('^\S\+')+1+v:count)<CR>
         nnoremap <buffer> <silent> D    :<C-u>exe "vertical resize ".(<SID>linechars('.\{-\}\ze\d\ze\s\+\d\+)')+1-v:count)<CR>
@@ -4916,10 +4888,10 @@ function! fugitive#BlameSyntax() abort
     endif
     exe 'syn match FugitiveblameHash'.hash.'       "\%(^\^\=\)\@<='.hash.'\x\{1,34\}\>" nextgroup=FugitiveblameAnnotation,FugitiveblameOriginalLineNumber,fugitiveblameOriginalFile skipwhite'
   endfor
-  call s:RehighlightBlame()
+  call s:BlameRehighlight()
 endfunction
 
-function! s:RehighlightBlame() abort
+function! s:BlameRehighlight() abort
   for [hash, cterm] in items(s:hash_colors)
     if !empty(cterm) || has('gui_running') || has('termguicolors') && &termguicolors
       exe 'hi FugitiveblameHash'.hash.' guifg=#'.hash.get(s:hash_colors, hash, '')
@@ -4929,6 +4901,47 @@ function! s:RehighlightBlame() abort
   endfor
 endfunction
 
+function! s:BlameFileType() abort
+  setlocal nomodeline
+  setlocal foldmethod=manual
+  if len(s:Dir())
+    let &l:keywordprg = s:Keywordprg()
+  endif
+  let b:undo_ftplugin = 'setl keywordprg= foldmethod<'
+  if exists('+concealcursor')
+    setlocal concealcursor=nc conceallevel=2
+    let b:undo_ftplugin .= ' concealcursor< conceallevel<'
+  endif
+  if &modifiable
+    return ''
+  endif
+  nnoremap <buffer> <silent> <F1> :help fugitive-:Gblame<CR>
+  nnoremap <buffer> <silent> g?   :help fugitive-:Gblame<CR>
+  if mapcheck('q', 'n') =~# '^$\|bdelete'
+    nnoremap <buffer> <silent> q    :exe <SID>BlameQuit()<Bar>echohl WarningMsg<Bar>echo ":Gblame q is deprecated in favor of gq"<Bar>echohl NONE<CR>
+  endif
+  exe 'nnoremap <buffer> <silent>' s:nowait "gq :exe <SID>BlameQuit()<CR>"
+  nnoremap <buffer> <silent> <CR> :<C-U>exe <SID>BlameCommit("exe <SID>BlameLeave()<Bar>edit")<CR>
+  nnoremap <buffer> <silent> -    :<C-U>exe <SID>BlameJump('')<CR>
+  nnoremap <buffer> <silent> P    :<C-U>exe <SID>BlameJump('^'.v:count1)<CR>
+  nnoremap <buffer> <silent> ~    :<C-U>exe <SID>BlameJump('~'.v:count1)<CR>
+  nnoremap <buffer> <silent> i    :<C-U>exe <SID>BlameCommit("exe <SID>BlameLeave()<Bar>edit")<CR>
+  nnoremap <buffer> <silent> o    :<C-U>exe <SID>BlameCommit("split")<CR>
+  nnoremap <buffer> <silent> O    :<C-U>exe <SID>BlameCommit("tabedit")<CR>
+  nnoremap <buffer> <silent> p    :<C-U>exe <SID>BlameCommit("pedit")<CR>
+endfunction
+
+augroup fugitive_blame
+  autocmd!
+  autocmd FileType fugitiveblame call s:BlameFileType()
+  autocmd User Fugitive
+        \ if get(b:, 'fugitive_type') =~# '^\%(file\|blob\)$' || s:BlameBufnr() > 0 || filereadable(@%) |
+        \   exe "command! -buffer -bar -bang -range=-1 -nargs=* -complete=customlist,s:BlameComplete Gblame :execute s:BlameCommand(<line1>,<line2>,+'<range>',<count>,<bang>0,'<mods>',<q-reg>,<q-args>,[<f-args>])" |
+        \ endif
+  autocmd ColorScheme,GUIEnter * call s:BlameRehighlight()
+  autocmd BufWinLeave * execute getwinvar(+bufwinnr(+expand('<abuf>')), 'fugitive_leave')
+augroup END
+
 " Section: :Gbrowse
 
 call s:command("-bar -bang -range=-1 -nargs=* -complete=customlist,fugitive#CompleteObject Gbrowse", "Browse")