Fix compilation error for osx.

Without specifying the osx deployment target you are not able to pod
install on osx.
Merge pull request #2 from keisi/2.2

Fix compilation error for OS X.
Revert progress block signatures because of AFNetworking 2.2.3.

This reverts commit c6065bd3fafe2fcda9c564175673e21d50eedded.
Merge branch 'session_token' into all_patches
Merge remote-tracking branch 'evoL/2.2-all_patches' into patches