Prepare testsuite for a "git clone" that packs refs

t5515-fetch-merge-logic removes many, but not all, refs between each test.
This is done by removing the corresponding refs/foo/* files in the .git/refs
hierarchy. However, once "git clone" starts producing packed refs, these refs
will no longer be in the .git/refs hierarchy, but rather listed in
.git/packed-refs. This patch teaches t5515-fetch-merge-logic to remove the
refs using "git update-ref -d" which properly handles packed refs.

Signed-off-by: Johan Herland <johan@herland.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t5515-fetch-merge-logic.sh

@@ -142,9 +142,12 @@ do
 			set x $cmd; shift
 			git symbolic-ref HEAD refs/heads/$1 ; shift
 			rm -f .git/FETCH_HEAD
-			rm -f .git/refs/heads/*
-			rm -f .git/refs/remotes/rem/*
-			rm -f .git/refs/tags/*
+			git for-each-ref \
+				refs/heads refs/remotes/rem refs/tags |
+			while read val type refname
+			do
+				git update-ref -d "$refname" "$val"
+			done
 			git fetch "$@" >/dev/null
 			cat .git/FETCH_HEAD
 		} >"$actual_f" &&