Include git notes in commit buffers

Issue #912

Calling "git notes list" serves both to suppress the "Notes:" prefix when a
commit does not have any notes, and to avoid using notes formats in older
versions of git.

Author: a-m-s

autoload/fugitive.vim

@@ -2031,7 +2031,9 @@ 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])
+          let [note, exec_error] = s:ChompError([dir, 'notes', 'list', rev])
+          let noteformat = (exec_error ? '' : '%nNotes:%n%N')
+          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' . noteformat, rev])
           keepjumps call search('^parent ')
           if getline('.') ==# 'parent '
             silent keepjumps delete_