Fix up default abbrev in setup_revisions() argument parser.

The default abbreviation precision should be DEFAULT_ABBREV as before.
Signed-off-by: NJunio C Hamano <junkio@cox.net>

diff-tree.c

@@ -69,6 +69,7 @@ int main(int argc, const char **argv)
 
 	git_config(git_diff_config);
 	nr_sha1 = 0;
+	opt->abbrev = 0;
 	argc = setup_revisions(argc, argv, opt, NULL);
 
 	while (--argc > 0) {

git.c

@@ -286,6 +286,7 @@ static int cmd_log(int argc, const char **argv, char **envp)
 	const char *commit_prefix = "commit ";
 	int shown = 0;
 
+	rev.abbrev = DEFAULT_ABBREV;
 	argc = setup_revisions(argc, argv, &rev, "HEAD");
 	if (argc > 1)
 		die("unrecognized argument: %s", argv[1]);

revision.c

@@ -475,7 +475,12 @@ static void handle_all(struct rev_info *revs, unsigned flags)
 
 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;