t/gitweb-lib: Split HTTP response with non-GNU sed

t/gitweb-lib: Split HTTP response with non-GNU sed

Recognizing \r in a regex is something GNU sed will do, but other sed
implementation's won't (e.g. BSD sed on OS X).  Instead of two sed
invocations, use a single Perl script to split output into headers
and body.

Signed-off-by: Brian Gernhardt <brian@gernhardtsoftware.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>