refs: move REF_DELETING to refs.c

It is only used internally now. Document it a little bit better, too.
Signed-off-by: NMichael Haggerty <mhagger@alum.mit.edu>
Reviewed-by: NStefan Beller <sbeller@google.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

refs.c

@@ -34,6 +34,12 @@ static unsigned char refname_disposition[256] = {
 	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 3, 0, 0, 4, 4
 };
 
+/*
+ * Flag passed to lock_ref_sha1_basic() telling it to tolerate broken
+ * refs (i.e., because the reference is about to be deleted anyway).
+ */
+#define REF_DELETING	0x02
+
 /*
  * Used as a flag to ref_transaction_delete when a loose ref is being
  * pruned.

refs.h

@@ -183,12 +183,10 @@ extern int peel_ref(const char *refname, unsigned char *sha1);
  * Flags controlling ref_transaction_update(), ref_transaction_create(), etc.
  * REF_NODEREF: act on the ref directly, instead of dereferencing
  *              symbolic references.
- * REF_DELETING: tolerate broken refs
  *
- * Flags >= 0x100 are reserved for internal use.
+ * Other flags are reserved for internal use.
  */
 #define REF_NODEREF	0x01
-#define REF_DELETING	0x02
 
 /*
  * Setup reflog before using. Set errno to something meaningful on failure.