Support for qtranslate and custom translation pattern in the Wordpress import plugin

qtranslate (http://wordpress.org/plugins/qtranslate/) is a very popular Wordpress plugin for writing multilingual blogs and since this same feature is an important piece of Nikola, this code change makes it possible to import qtranslate-based multilingual Wordpress blogs to Nikola.

NOTE: to be able to do so by avoiding adding ugly hardcoded stuff I had to access the default translations pattern from the plugin. I did it by adding a global variable to nikola.py (where the pattern was already hardcoded anyway). This is a debatable practice I guess :) and that's why I'm calling your attention to it. Feel free to indicate me a better way if needed.