Fix iOS 8 support and use libc++ instead of libstdc++
Add sdk 7.1 and 8 to build-mailcore2-ios
Merge branch 'master' of https://github.com/MailCore/mailcore2 into iOS8AndLibCpp
Merge pull request #807 from gnachman/iOS8AndLibCpp

Add support for building against iOS 8 SDK. Use libc++ instead of libstdc++.