Fix apps loading

Currently, one you add apps in the apps/ directory, you need to call them with 'apps.$app', that sucks. :-) The first commit solves this.

Also, if you get an __init__.pyc file, it will get taken as an app, the second commit fixes that. Maybe the function should only take directories instead of this workaround though.
`PROJECT_APPS` needs to be a tuple or you'll get an error when generating `INSTALLED_APPS` (since you can't concatenate a tuple and a list). Just add a `tuple()` around the expression and I'll merge it. Thanks!