cache.h: remove dependence on hex.h; make other files include it explicitly

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/remote.c b/remote.c
index daade49..b04e5da 100644
--- a/remote.c
+++ b/remote.c
@@ -1,6 +1,7 @@
 #include "git-compat-util.h"
 #include "alloc.h"
 #include "config.h"
+#include "hex.h"
 #include "remote.h"
 #include "urlmatch.h"
 #include "refs.h"