Can not look-up language dependant aliases

Problem/Motivation

When importing a language undefined csv to alias that specify a language, the alias lookup fails

Example:
CSV:

from,to
old-alias,node-alias

url_alias table:

pid,source,alias,language
1,node/1,node-alias,en

What the alias lookup happens it specifies the language code 'und'. This fails to match the 'en' version of the alias.

Proposed resolution

Do a language independent alias lookup asking for a language code of '' (empty string).