Ignore E302 "Could not rename swap file" error

According to `:help E302`, E302 comes from Vim being unable to rename
the swap file when an open buffer's name is changed; but the error is
mostly harmless. E302 seems to occur in vim-fugitive under Windows but
not *nix.

This fix allow :Glog and :Gdiff to work on such systems; previously the
uncaught error made these operations fail or at least work strangely.

plugin/fugitive.vim

@@ -2078,7 +2078,10 @@ function! s:ReplaceCmd(cmd,...) abort
   try
     silent edit!
   finally
-    silent exe 'keepalt file '.s:fnameescape(fn)
+    try
+      silent exe 'keepalt file '.s:fnameescape(fn)
+    catch /^Vim\%((\a\+)\)\=:E302/
+    endtry
     call delete(tmp)
     if fnamemodify(bufname('$'), ':p') ==# tmp
       silent execute 'bwipeout '.bufnr('$')