Use importlib for url prefixing function

This will allow for django style syntax, where you can import a module with dot syntax.
Update README and test_settings
Python 2.7 is required

importlibs was only implemented in 2.7 and up.
Use load_module over import_module

There is better cross python support
Use __import__

It seems to be the only way to import a module, defined as a string, in Python 2.6

http://stackoverflow.com/questions/8718885/import-module-from-string-variable
add settings.
Use custom import

Because 2.6 and 2.7 have different module loading and various versions of django do as well - it is necessary to have this custom import.
Use django import_module

import_module is available in 1.4 and up. It is still necessary to gettattr to call the individual method.
Fix typo
Simplify rpartition indexing
Insure there are not empty stings in the whitelisted tuple

An empty sting will cause djstopie to not redirect an unsupported browser - this is possible if the setting.MEDIA_URL is not set
Improve naming
Merge pull request #4 from yola/use_import_lib

Use importlibs