object.h: stop depending on cache.h; make cache.h depend on object.h

Things should be able to depend on object.h without pulling in all of
cache.h.  Move an enum to allow this.

Note that a couple files previously depended on things brought in
through cache.h indirectly (revision.h -> commit.h -> object.h ->
cache.h).  As such, this change requires making existing dependencies
more explicit in half a dozen files.  The inclusion of strbuf.h in
some headers if of particular note: these headers directly embedded a
strbuf in some new structs, meaning they should have been including
strbuf.h all along but were indirectly getting the necessary
definitions.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

object.h

@@ -1,7 +1,7 @@
 #ifndef OBJECT_H
 #define OBJECT_H
 
-#include "cache.h"
+#include "hash.h"
 
 struct buffer_slab;
 
@@ -81,6 +81,26 @@ struct object_array {
  */
 #define FLAG_BITS  28
 
+#define TYPE_BITS 3
+
+/*
+ * Values in this enum (except those outside the 3 bit range) are part
+ * of pack file format. See gitformat-pack(5) for more information.
+ */
+enum object_type {
+	OBJ_BAD = -1,
+	OBJ_NONE = 0,
+	OBJ_COMMIT = 1,
+	OBJ_TREE = 2,
+	OBJ_BLOB = 3,
+	OBJ_TAG = 4,
+	/* 5 for future expansion */
+	OBJ_OFS_DELTA = 6,
+	OBJ_REF_DELTA = 7,
+	OBJ_ANY,
+	OBJ_MAX
+};
+
 /*
  * The object type is stored in 3 bits.
  */