Include git notes in commit buffers

Issue #912

Add any existing git notes into commit views, between the commit message and
the patch itself.  This is similar to what "git show" does, albeit without any
indent.

This should work for older versions of git, without the notes feature,
provided that the '%N' directive is passed through as-is.

autoload/fugitive.vim

@@ -2031,7 +2031,11 @@ function! fugitive#BufReadCmd(...) abort
         if b:fugitive_display_format
           call s:ReplaceCmd([dir, 'cat-file', b:fugitive_type, rev])
         else
-          call s:ReplaceCmd([dir, 'show', '--no-color', '-m', '--first-parent', '--pretty=format:tree%x20%T%nparent%x20%P%nauthor%x20%an%x20<%ae>%x20%ad%ncommitter%x20%cn%x20<%ce>%x20%cd%nencoding%x20%e%n%n%s%n%n%b', rev])
+          call s:ReplaceCmd([dir, 'show', '--no-color', '-m', '--first-parent', '--pretty=format:tree%x20%T%nparent%x20%P%nauthor%x20%an%x20<%ae>%x20%ad%ncommitter%x20%cn%x20<%ce>%x20%cd%nencoding%x20%e%n%n%s%n%n%b%nFuGiTiVeBeGiNmArKeRNotes:%n%NFuGiTiVeEnDmArKeR', rev])
+	  silent! keepjumps g/FuGiTiVeEnDmArKeR/norm! kgJ
+	  silent! keepjumps g/^FuGiTiVeBeGiNmArKeRNotes:\(%N\)\?FuGiTiVeEnDmArKeR$/d
+	  silent! keepjumps %s/^FuGiTiVeBeGiNmArKeR//
+	  silent! keepjumps %s/FuGiTiVeEnDmArKeR$//
           keepjumps call search('^parent ')
           if getline('.') ==# 'parent '
             silent keepjumps delete_