Forced application/json Content-Type to include a charset, as application expects.  Revert "Fixed a bug where JSON/JSONP was returning an invalid ``charset`` within the MIME type. Thanks to dstufft for the report!"

This reverts commit 609f2e29b3b0055dc1081f2fc138643e34716fb3.

Conflicts:
	tastypie/utils/mime.py
	tests/core/tests/utils.py