hgweb: fix broken URLs of RSS/Atom feeds (
issue1772)
This fixes doubled URL, e.g. http://example.orghttp://example.org/...,
which appears on RSS/Atom feeds served by hgwebdir.
It splits baseurl to update SERVER_NAME, SERVER_PORT and SCRIPT_NAME,
according to RFC 3875.
Updated the test output since SCRIPT_NAME becomes not to contain
http://host:port part.