checkout: pass the "num_matches" up to callers

Pass the previously added "num_matches" struct value up to the callers
of unique_tracking_name(). This will allow callers to optionally print
better error messages in a later change.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

checkout.h

@@ -9,6 +9,7 @@
  * exists, NULL otherwise.
  */
 extern const char *unique_tracking_name(const char *name,
-					struct object_id *oid);
+					struct object_id *oid,
+					int *dwim_remotes_matched);
 
 #endif /* CHECKOUT_H */