Base path should be used to determine whether or not a file is local

This patch edits the module to use the base path when determining whether a file is local or remote. For cases in which Drupal is installed at a URL like example.org/drupal, the filter should treat files originating from URLs such as example.org/not-drupal/img.jpg as though they were remote files. The main reason for this is that when Drupal fetches the file for caching/resizing, you don't want it to use a relative URL like /drupal/not-drupal/img.jpg; instead you want to use an absolute URL: http://example.org/not-drupal/img.jpg.

In the unpatched code, the preg_replace on line 324 (331 of the patched file) checks for the existence of the domain plus base path in the image path, and replaces it with a blank. The unpatched code would treat an image at http://example.org/not-drupal/img.jpg as local (because it starts with http://example.org), but the aforementioned regex would fail to match, and you'd end up with a URL rather than a filepath when you get to is_file() further down the function.

Anyway, I've tested this patch and it resolves the issue on sites installed in a subdirectory, without hurting sites installed at the root of a domain. The patch was rolled according to these instructions: http://drupal.org/node/337087/git-instructions/6.x-1.x. If I was supposed to run them according to http://drupal.org/node/337087/git-instructions/master instead, let me know and I'll run it again.