revision: replace use of hard-coded constants

Replace two uses of the hard-coded constant 40 with references to
the_hash_algo.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

revision.c

@@ -1751,6 +1751,7 @@ static int handle_revision_opt(struct rev_info *revs, int argc, const char **arg
 	const char *arg = argv[0];
 	const char *optarg;
 	int argcount;
+	const unsigned hexsz = the_hash_algo->hexsz;
 
 	/* pseudo revision arguments */
 	if (!strcmp(arg, "--all") || !strcmp(arg, "--branches") ||
@@ -2038,8 +2039,8 @@ static int handle_revision_opt(struct rev_info *revs, int argc, const char **arg
 		revs->abbrev = strtoul(optarg, NULL, 10);
 		if (revs->abbrev < MINIMUM_ABBREV)
 			revs->abbrev = MINIMUM_ABBREV;
-		else if (revs->abbrev > 40)
-			revs->abbrev = 40;
+		else if (revs->abbrev > hexsz)
+			revs->abbrev = hexsz;
 	} else if (!strcmp(arg, "--abbrev-commit")) {
 		revs->abbrev_commit = 1;
 		revs->abbrev_commit_given = 1;