Begin phasing out :Git --paginate special case

This was a mistake.  I took --paginate to be the opposite of --no-pager,
but it forces $PAGER over $GIT_PAGER and pager configuration.  This
defeats the purpose of using it as way to trick :Git into running a
regular command with :terminal.

References https://github.com/tpope/vim-fugitive/issues/1415

README.markdown

@@ -92,9 +92,8 @@ request the password via a GUI.  Fugitive will configure this for you
 automatically if you have `ssh-askpass` or `git-gui` installed; otherwise it's
 your responsibility to set this up.
 
-As an absolute last resort, you can invoke `:Git --paginate push`.  Fugitive
-recognizes the pagination request and fires up a `:terminal`, which allows for
-interactive password entry.
+If you absolutely must type in your password by hand, sidestep Fugitive and
+use `:terminal git push`.
 
 [credentials caching]: https://help.github.com/en/articles/caching-your-github-password-in-git
 

autoload/fugitive.vim

@@ -2192,6 +2192,10 @@ function! fugitive#Command(line1, line2, range, bang, mods, arg) abort
         \ (args[0] ==# 'help' || get(args, 1, '') ==# '--help') && !s:HasOpt(args, '--web')
     return s:OpenExec((a:line2 > 0 ? a:line2 : '') . (a:line2 ? 'split' : 'edit'), a:mods, args, dir) . after
   endif
+  if index(['--paginate', '-p'], args[0]) >= 0
+    let paginate_warning = 'fugitive: --paginate support is deprecated. Use :terminal directly'
+    let after = '|echohl WarningMsg|echo ' . string(paginate_warning) . '|echohl NONE' . after
+  endif
   if s:HasOpt(args, ['add', 'checkout', 'commit', 'stage', 'stash', 'reset'], '-p', '--patch') ||
         \ s:HasOpt(args, ['add', 'clean', 'stage'], '-i', '--interactive') ||
         \ index(['--paginate', '-p'], args[0]) >= 0