Handle deficiencies in PHP's parse_url in older versions of PHP (<5.4.7) in WP_HTTP::make_absolute_url().

In older versions of PHP:
- parse_url() will fail to parse a url where the scheme break (://) is present in a relative URL's path
- parse_url() will include the hostname of a schemeless URL in the path component

This handles those two types of URL's by correcting the response from parse_url().

Fixes #28001, #29886


git-svn-id: https://develop.svn.wordpress.org/trunk@29861 602fd350-edb4-49c9-b593-d223f7449a82