Simplify test execution by leveraging `buildImplicitDependencies=YES` (requires xctool >= 0.1.6)
Install xctool directly from unmerged 0.1.7 formula since --HEAD is broken
Uninstall previous version of xctool before installing 0.1.7
Bump AFNetworking submodule reference to 1.3.1
Pass the default `NSURLCredential` through from the underlying `AFHTTPClient` to the HTTP operations that underly object request operations. refs #1480