add diff_flush_patch_id() to calculate the patch id

Call it like this:

unsigned char id[20];
if (diff_flush_patch_id(diff_options, id))
	printf("And the patch id is: %s\n", sha1_to_hex(id));

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

1 files changed, 2 insertions, 0 deletions

diff --git a/diff.h b/diff.h
index b61fdc8f1e..d5068af7d1 100644
--- a/diff.h
+++ b/diff.h
@@ -184,4 +184,6 @@ extern int run_diff_files(struct rev_info *revs, int silent_on_removed);
 
 extern int run_diff_index(struct rev_info *revs, int cached);
 
+extern int diff_flush_patch_id(struct diff_options *, unsigned char *);
+
 #endif /* DIFF_H */