Path aliases don't always work when translation module is enabled

To reproduce this bug:
- Translation module enabled and add the foo language, and make it the default language.
- Select English as language in your profile.
- Create a content type with 'Multilingual support' disabled
- Create a node with an alias
- Try to surf to the newly created node using the alias

Result:
'Page not found' error

Expected result:
The node is displayed

Cause:
When a node is saved, but multilingual support is disabled, the node is saved with the default language foo. This causes the alias to be saved with the language foo as well.
When looking up the path, the alias is searched with the current language (english) and with LANGUAGE_NONE. Both are not found.

Proposed fix:
When a node is saved for a type without multilingual support, use LANGUAGE_NONE as the language for the node