Add failure handlers to test calls.
Merge pull request #1697 from carsonmcdonald/capturetestfailures

Add failure handlers to test calls.
Ignoring -Wunused-parameter for AFContentTypeForPathExtension
Enabling additional warnings
Merge branch 'master' of github.com:AFNetworking/AFNetworking
[Issue #1701] Validating responses of download tasks
Update CONTRIBUTING.md
Update CONTRIBUTING.md
Removing unnecessary != NULL for error pointer check, for consistency
Merge branch 'master' of github.com:AFNetworking/AFNetworking
Merge live