Teach git-diff-files the new option `--no-index`

With this flag and given two paths, git-diff-files behaves as a GNU diff
lookalike (plus the git goodies like --check, colour, etc.).  This flag
is also available in git-diff.  It also works outside of a git repository.

In addition, if git-diff{,-files} is called without revision or stage
parameter, and with exactly two paths at least one of which is not tracked,
the default is --no-index.

So, you can now say

	git diff /etc/inittab /etc/fstab

and it actually works!

This also unifies the duplicated argument parsing between cmd_diff_files()
and builtin_diff_files().

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <junkio@cox.net>

1 files changed, 2 insertions, 1 deletions

diff --git a/diff.c b/diff.c
index 12c8b2b87..701880aba 100644
--- a/diff.c
+++ b/diff.c
@@ -2406,7 +2406,8 @@ static void diff_resolve_rename_copy(void)
 				p->status = DIFF_STATUS_RENAMED;
 		}
 		else if (hashcmp(p->one->sha1, p->two->sha1) ||
-			 p->one->mode != p->two->mode)
+			 p->one->mode != p->two->mode ||
+			 is_null_sha1(p->one->sha1))
 			p->status = DIFF_STATUS_MODIFIED;
 		else {
 			/* This is a "no-change" entry and should not