Rewrite path matching code

Issue Summary

Currently in path_redirect_check(), we first match a redirect by the current path with query string. If a match was not found, then we search by just the current path without the query string. The majority of redirects that users have do not involve redirects, so this creates an extra query for every hook_init() call. For a large site with a large number of redirects, this could be optimized to match just by the path alone first, then path with the query string.

This will also allow us to use the prepared $_GET['q'] variable since it just contains the path element instead of finagling with request_uri(). This will also have slight performance increase for large sites on every hook_init() call.

I'm looking into implementing this change. As a part of this, the current path field in {path_redirect} will need to be split into two fields, a path and a path_query field. As a part of this split, I'd like to do a clean-up on the current field names since we'll now have two query fields. The proposed changes to {path_redirect} table fields are as follows:

path -> src and src_query
redirect -> dst
query -> dst_query
fragment -> dst_fragment

Now we'd be using 'src' and 'dst' just like {url_alias}, will be a little easier to understand, and should be fairly future-proof.