Merge branch 'jc/fetch-raw-sha1'

Allows requests to fetch objects at any tip of refs (including
hidden ones).  It seems that there may be use cases even outside
Gerrit (e.g. $gmane/215701).

* jc/fetch-raw-sha1:
  fetch: fetch objects by their exact SHA-1 object names
  upload-pack: optionally allow fetching from the tips of hidden refs
  fetch: use struct ref to represent refs to be fetched
  parse_fetch_refspec(): clarify the codeflow a bit

cache.h

@@ -1017,7 +1017,8 @@ struct ref {
 		force:1,
 		forced_update:1,
 		merge:1,
-		deletion:1;
+		deletion:1,
+		matched:1;
 	enum {
 		REF_STATUS_NONE = 0,
 		REF_STATUS_OK,