Fix up default abbrev in setup_revisions() argument parser.

The default abbreviation precision should be DEFAULT_ABBREV as before.

Signed-off-by: Junio C Hamano <junkio@cox.net>
diff --git a/revision.c b/revision.c
index 1d26e0d..bdf8005 100644
--- a/revision.c
+++ b/revision.c
@@ -475,7 +475,12 @@
 
 void init_revisions(struct rev_info *revs)
 {
+	unsigned abbrev = revs->abbrev;
+
 	memset(revs, 0, sizeof(*revs));
+
+	revs->abbrev = abbrev;
+	revs->ignore_merges = 1;
 	revs->pruning.recursive = 1;
 	revs->pruning.add_remove = file_add_remove;
 	revs->pruning.change = file_change;