Support sub-directory installations

If I have an installation in a subdirectory, then the subdirectory gets added on twice when the URL is rewritten. So, a URL like "/subdir/node/1" would get rewritten to be "http://example.com/subdir/subdir/node/1".

I think the $base_path needs to searched for, instead of "/", and the following code should do it:

global $base_path;
$text = preg_replace(
  '/(src|href)=(\'|")' . preg_quote($base_path, '/') . '/',
  '$1=$2'. url('<front>', array('absolute' => TRUE, 'language' => $lang)),
  $text
);