Python 2.x Unicode support

In the tastypie/resources.py: Resource.method_check
```Python
def method_check(self, request, allowed=None):
        """
        Ensures that the HTTP method used on the request is allowed to be
        handled by the resource.

        Takes an ``allowed`` parameter, which should be a list of lowercase
        HTTP methods to check against. Usually, this looks like::

            # The most generic lookup.
            self.method_check(request, self._meta.allowed_methods)

            # A lookup against what's allowed for list-type methods.
            self.method_check(request, self._meta.list_allowed_methods)

            # A useful check when creating a new endpoint that only handles
            # GET.
            self.method_check(request, ['get'])
        """
        if allowed is None:
            allowed = []

        request_method = request.method.lower()
        allows = ','.join(map(str.upper, allowed))
```

The "allows" line is broken when I defined the allowed_methods in unicode form of Python 2.x.
For example:
```Python
from __future__ import unicode_literals
allowed_methods = ['get']
```

Probably can be solved with "six" which is shipped with django.
```Python
from django.utils.six import text_type
allows = ','.join(map(text_type.upper, allowed))
```