custom_url_rewrite only half written, produces wrong paths

i18n uses custom_url_rewrite() to give paths language-dependent aliases. This works when a module calls drupal_get_path_alias(). However, the parallel implementation is missing. drupal_get_normal_path() also invokes custom_url_rewrite(). i18n needs to respond, returning the normal path.

To put the case another way: every custom_url_rewrite() implementation should have not just one but two parts:

1. Respond to an 'alias' request as passed in by drupal_get_path_alias(), to convert an path into a new format.
2. Do the opposite: given what is potentially an alias, respond to a 'source' request as passed in by drupal_get_normal_path() and return the normal path.

This error has come up e.g., in this bug, http://drupal.org/node/96934.

The fix is easy. We already have the needed function, i18n_get_normal_path(). All we need to do is add a call to this to the custom_url_rewrite() implementation.

Patch attached. This patch fixes the issue in activemenu module.