format-patch: give --reroll-count a short synonym -v

Accept "-v" as a synonym to "--reroll-count", so that users can say
"git format-patch -v4 master", instead of having to fully spell it
out as "git format-patch --reroll-count=4 master".

As I do not think of a reason why users would want to tell the
command to be "verbose", I think this should be OK.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/log.c

@@ -1081,7 +1081,7 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
 			    N_("use <sfx> instead of '.patch'")),
 		OPT_INTEGER(0, "start-number", &start_number,
 			    N_("start numbering patches at <n> instead of 1")),
-		OPT_INTEGER(0, "reroll-count", &reroll_count,
+		OPT_INTEGER('v', "reroll-count", &reroll_count,
 			    N_("mark the series as Nth re-roll")),
 		{ OPTION_CALLBACK, 0, "subject-prefix", &rev, N_("prefix"),
 			    N_("Use [<prefix>] instead of [PATCH]"),