Simplify logic to generate home path when parsing request

[evansolomon]

In WP::parse_request() we go through a few steps to generate the $home_path variable. Since we now require PHP 5.2, we can use parse_url()'s second argument to get the path directly.

[scribu]

That whole area could use some cleanup.

Like, replacing this:

$req_uri_array = explode('?', $req_uri);
$req_uri = $req_uri_array[0];

with this:

list( $req_uri ) = explode( '?', $req_uri );

or maybe even using parse_str().

[wonderboymusic]

Patch still applies - more cleanup code be done, but this works

[nacin]

In 25617:

Clean up the path calculations in wp::parse_request().

props evansolomon for initial cleanup.
fixes #22209.