Include mailmap.h in mailmap.c to catch mailmap interface changes

Signed-off-by: Alex Riesen <raa.lkml@gmail.com>
Signed-off-by: Junio C Hamano <junkio@cox.net>

mailmap.c

@@ -1,5 +1,6 @@
 #include "cache.h"
 #include "path-list.h"
+#include "mailmap.h"
 
 int read_mailmap(struct path_list *map, const char *filename, char **repo_abbrev)
 {