Make resource._meta.detail_uri_name backwards compatible with TastyPie 0.9.11
Fix bug which causes JSON serialization error

The ``help_text`` is a Django proxy, and without this fix (on
Django==1.4.2, TastyPie==0.9.11) a JSON serialization error is raised::

    TypeError: <django.utils.functional.__proxy__ object at 0x103c09450> is not JSON serializable
Use force_unicode instead of unicode
Merge pull request #21 from wolever/master

Fix a couple crashing bugs with TastyPie==0.9.11 and Django==1.4.2