add plumbing for update fetch head on remotes

remote.go

@@ -433,6 +433,14 @@ func (o *Remote) RefspecCount() uint {
 	return uint(C.git_remote_refspec_count(o.ptr))
 }
 
+func (o *Remote) SetUpdateFetchHead(val bool) {
+        C.git_remote_set_update_fetchhead(o.ptr, cbool(val))
+}
+
+func (o *Remote) UpdateFetchHead() bool {
+        return C.git_remote_update_fetchhead(o.ptr) > 0
+}
+
 func (o *Remote) Fetch(sig *Signature, msg string) error {
 
 	var csig *C.git_signature = nil

vendor/libgit2

@@ -1 +1 @@
-Subproject commit 89e05e2ab19ac452e84e0eaa2dfb8e07ac6839bf
+Subproject commit e0383fa35f981c656043976a43c61bff059cb709