diff: teach diff to display submodule difference with an inline diff

Teach git-diff and friends a new format for displaying the difference
of a submodule. The new format is an inline diff of the contents of the
submodule between the commit range of the update. This allows the user
to see the actual code change caused by a submodule update.

Add tests for the new format and option.

Signed-off-by: Jacob Keller <jacob.keller@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/diff.h b/diff.h
index 14be35d01..2d884f1d0 100644
--- a/diff.h
+++ b/diff.h
@@ -111,7 +111,8 @@ enum diff_words_type {
 
 enum diff_submodule_format {
 	DIFF_SUBMODULE_SHORT = 0,
-	DIFF_SUBMODULE_LOG
+	DIFF_SUBMODULE_LOG,
+	DIFF_SUBMODULE_INLINE_DIFF
 };
 
 struct diff_options {