import all locales in single xpi file

[Kyle Nitzsche]

Some mozilla xpi applications (like webfav) have their xpi structured as a single xpi file that contains many/all locales. But, The importer currently only treats the xpi as containing the single locale defined by the xpi's file name. For example, en-US.xpi is imported as only en-US, even though it may contain a large number of other locales.

This bug suggests that Rosetta looks inside the xpi and imports all locales contained in it, instead of trying to import the single contained locale that is specified in the xpi filename.