Stable/0.3.x: Fix @api_view wrapper detection on DRF 3.4.7+

[tuffnatty]

Since the merge of encode/django-rest-framework@5df54a7, functions wrapped with @api_view decorator could no longer be detected which resulted in failing tests.

[tuffnatty]

@marcgibbons As soon as this PR is merged, my other PRs (#650, #651, #652, #653, #655, #685, #686, #687, #688, #689, #690, #692) as well as other people's PRs against the stable/0.3.x branch will also pass testing.