Configurable white-list for $parts['scheme'], which will allow schema links to be passed to hook_pathologic_alter()

Pathologic has hardcoded in a white-list of schemes to pass onto hook_pathologic_alter() functions. Problem is, if you want to use hook_pathologic_alter() to alter a link other than http, https, file, internal, currently that's not possible.

These can be found in pathologic.module line ~190 in `_pathologic_replace()`

  $parts = parse_url($original_url);
  // Do some more early tests to see if we should just give up now.
  if (
    // If parse_url() failed, give up.
    $parts === FALSE ||
    // If there's a scheme part and it doesn't look useful, bail out.
    // "files" and "internal" are for Path Filter compatibility.
    (isset($parts['scheme']) && !in_array($parts['scheme'], array('http', 'https', 'files', 'internal')))
  ) {
    // Give up by "replacing" the original with the same.
    return $matches[0];
  }

My site heavily relies on UUIDs and I'd like to use them for links using a schema path. I know in the documentation you mention you don't like the use of things like internal: and such...but I personally do, so I'd like to use uuid:. Don't feel like writing an entire input filter, if I can continue to use pathologic to do it via hooks. Much easier for dev/administrative maintenance.

Problem is, when I use uuid:, pathologic won't pass on this schema to hook_pathologic_alter() since it's not whitelisted.

To change this, we can change the whitelist to be a variable_get() to provide more flexibility.

Would look something like this

  $parts = parse_url($original_url);
  // Do some more early tests to see if we should just give up now.
  if (
    // If parse_url() failed, give up.
    $parts === FALSE ||
    // If there's a scheme part and it doesn't look useful, bail out.
    // "files" and "internal" are for Path Filter compatibility.
    (isset($parts['scheme']) && !in_array($parts['scheme'], variable_get('pathologic_schema_whitelist', array('http', 'https', 'files', 'internal'))))
  ) {
    // Give up by "replacing" the original with the same.
    return $matches[0];
  }

Included is a patch which is the same code. I've tried to reformat the code for readability & comments, while staying under 80 chars per line. Matter of taste, but take a look.