Newer versions of Perl produce the warning "Unescaped left brace in
regex is deprecated, passed through in regex" when an unescaped left
brace occurs in a regex. Escape the brace to avoid this warning.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>