add_update(): initialize the whole ref_update

Change add_update() to initialize all of the fields in the new
ref_update object. Rename the function to ref_transaction_add_update(),
and increase its visibility to all of the refs-related code.

All of this makes the function more useful for other future callers.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>

refs/refs-internal.h

@@ -157,6 +157,20 @@ struct ref_update {
 	const char refname[FLEX_ARRAY];
 };
 
+/*
+ * Add a ref_update with the specified properties to transaction, and
+ * return a pointer to the new object. This function does not verify
+ * that refname is well-formed. new_sha1 and old_sha1 are only
+ * dereferenced if the REF_HAVE_NEW and REF_HAVE_OLD bits,
+ * respectively, are set in flags.
+ */
+struct ref_update *ref_transaction_add_update(
+		struct ref_transaction *transaction,
+		const char *refname, unsigned int flags,
+		const unsigned char *new_sha1,
+		const unsigned char *old_sha1,
+		const char *msg);
+
 /*
  * Transaction states.
  * OPEN:   The transaction is in a valid state and can accept new updates.