add Alamofire.xcscheme for Carthage support
not build AlamofireTests except for testing
OS X target support.

Conflicts:
	Tests/DownloadTests.swift
OS X target support - include i386 and x86_64 archs.
AlamofireOSX.framework product added.
Alamofire.framework for both iOS and OSX.
Inherit code sign from project.
iOS / OS X Default Signing Identities