Fix Bug 1101261 - Visiting www.mozilla.org/firefox/new/ (and others) with an es browser leads to /es-AR/ page.

@pmclanahan if another site already had a CANONICAL_LOCALES setting in their site's settings/base.py or settings/local.py, it's my understanding that it would override the one here; is there something I'm missing? Also, I did some searching, and I couldn't find any projects using funfactory that have a CANONICAL_LOCALES setting already.