Add --relative-date option to the revision interface

Exposes the infrastructure from 9a8e35e98793af086f05d1ca9643052df9b44a74.

Signed-off-by: Jonas Fonseca <fonseca@diku.dk>
Signed-off-by: Junio C Hamano <junkio@cox.net>
diff --git a/log-tree.c b/log-tree.c
index 031af88..54cdaa4 100644
--- a/log-tree.c
+++ b/log-tree.c
@@ -194,7 +194,9 @@
 	/*
 	 * And then the pretty-printed message itself
 	 */
-	len = pretty_print_commit(opt->commit_format, commit, ~0u, this_header, sizeof(this_header), abbrev, subject, extra_headers);
+	len = pretty_print_commit(opt->commit_format, commit, ~0u, this_header,
+				  sizeof(this_header), abbrev, subject,
+				  extra_headers, opt->relative_date);
 
 	if (opt->add_signoff)
 		len = append_signoff(this_header, sizeof(this_header), len,