Import force_bytes on django >= 1.5
Add file upload test for APIRequestFactory

Remove test_compat
Remove TODO note, since it hasn't been TODONE.
Only add 'Vary: Accept' header when there is more than one possible renderer.
Use bytes BOUNDARY on django < 1.5

Django's encode_multipart was updated in django 1.5 to work internally
with unicode and convert to bytes.

In django >= 1.5 we therefore need to pass the BOUNDARY as unicode. In
django < 1.5 we still need to pass it as bytes.
Merge pull request #1377 from Ian-Foote/force_bytes

Import force_bytes on django >= 1.5