Implement applying the patch to the index using git-apply.
If a file is unchanged but stat-dirty, git-apply may erroneously fail to
apply patches, thinking that they conflict with a dirty working tree.
As such, since 2a6f08a (am: refresh the index at start and --resolved,
2011-08-15), git-am will refresh the index before applying patches.
Re-implement this behavior.
Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Paul Tan <pyokagan@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>