t5000: tar portability fix

The output of 'tar tv' varies from system to system. In
particular, the t5000 was expecting to parse the date from
something like:

  -rw-rw-r-- root/root         0 2008-05-13 04:27 file

but FreeBSD's tar produces this:

  -rw-rw-r--  0 root   root        0 May 13 04:27 file

Instead of relying on tar's output, let's just extract the
file using tar and stat the result using perl.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t5000-tar-tree.sh

@@ -67,10 +67,10 @@ test_expect_success \
 
 test_expect_success \
     'validate file modification time' \
-    'TZ=GMT $TAR tvf b.tar a/a |
-     awk \{print\ \$4,\ \(length\(\$5\)\<7\)\ ?\ \$5\":00\"\ :\ \$5\} \
-     >b.mtime &&
-     echo "2005-05-27 22:00:00" >expected.mtime &&
+    'mkdir extract &&
+     $TAR xf b.tar -C extract a/a &&
+     perl -e '\''print((stat("extract/a/a"))[9], "\n")'\'' >b.mtime &&
+     echo "1117231200" >expected.mtime &&
      diff expected.mtime b.mtime'
 
 test_expect_success \