Fix git {log,show,...} --pretty=email

An earlier --subject-prefix patch forgot that format-patch is
not the only codepath that adds the "[PATCH]" prefix, and broke
everybody else in the log family.

Signed-off-by: Junio C Hamano <junkio@cox.net>

revision.c

@@ -567,6 +567,7 @@ void init_revisions(struct rev_info *revs, const char *prefix)
 	revs->min_age = -1;
 	revs->skip_count = -1;
 	revs->max_count = -1;
+	revs->subject_prefix = "PATCH";
 
 	revs->prune_fn = NULL;
 	revs->prune_data = NULL;