t/gitweb-lib: use $PERL_PATH to run gitweb

The current code runs "perl gitweb.cgi" to test gitweb. This
will use whatever version of perl happens to be first in the
PATH. We are better off using the specific perl that the
user specified via PERL_PATH, which matches what gets put on
the #!-line of the built gitweb.cgi.

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

t/gitweb-lib.sh

@@ -68,7 +68,7 @@ gitweb_run () {
 	# written to web server logs, so we are not interested in that:
 	# we are interested only in properly formatted errors/warnings
 	rm -f gitweb.log &&
-	perl -- "$SCRIPT_NAME" \
+	"$PERL_PATH" -- "$SCRIPT_NAME" \
 		>gitweb.output 2>gitweb.log &&
 	perl -w -e '
 		open O, ">gitweb.headers";