alloc.h: move ALLOC_GROW() functions from cache.h

This allows us to replace includes of cache.h with includes of the much
smaller alloc.h in many places.  It does mean that we also need to add
includes of alloc.h in a number of C files.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/object-file.c b/object-file.c
index 939865c..18d6522 100644
--- a/object-file.c
+++ b/object-file.c
@@ -6,7 +6,8 @@
  * This handles basic git object files - packing, unpacking,
  * creation etc.
  */
-#include "cache.h"
+#include "git-compat-util.h"
+#include "alloc.h"
 #include "config.h"
 #include "string-list.h"
 #include "lockfile.h"