Changes from recompiling with xcode5

Added "Known Limitations" to README

Small changes in README

Unit Tests : Better messages when skipping tests (because classes not being available on the used target OS version)

Restored iOS6 Deployment Target for the Unit Tests, and added security for machines like Travis-CI still building with older SDK

Added Unit Tests for when NSURLSession uses a custom delegate (NSURLSessionDataDelegate)

Bumped to version 3.0.2

Prevent Unit Tests that involves NSURLSession to be run when we execute the Unit Tests by targeting iOS6 Simulator instead of iOS7 Simulator (as NSURLSession is not available in iOS6 which makes those tests pointless)

Fixing missing -ObjC flag in Unit Tests (making categories fail to load)

Fixing issue with cookies when nil request.URL on iOS6

Merge branch 'cookie-nil-url-unit-tests' of https://github.com/SBiOSoftWhare/OHHTTPStubs into SBiOSoftWhare-cookie-nil-url-unit-tests

Switching submodule back to original AFNetworking/AFNetworking.git now that my fork has been merged by mattt

Write unit tests in order to show a bad access issue on iOS 6.1 and below, when cookies are enabled and URL is nil on a request.

Trying to fix Xcode4/Travis-CI compilation error

Fixing conditional compilation macros (again), adding OSX_MAX_ALLOWED variant too and fixing Travis-CI's Xcode4 compilation error.