default core.clockskew variable to one day

This is the slop value used by name-rev, so presumably is a
reasonable default.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/tag.c

@@ -25,7 +25,7 @@ static const char * const git_tag_usage[] = {
 
 static char signingkey[1000];
 
-static int core_clock_skew = -1;
+static int core_clock_skew = 86400;
 
 struct tag_filter {
 	const char *pattern;