Foundation: correct handle management on URLSession
Foundation: correct handle management on URLSession

We would cast the CURL socket type to an Int and back during the
MultiHandle setup.  This does not work properly for Windows.  Given that
the interfaces are internal, keep the type sugar as far as possible
before handing off to libdispatch.

e78l/swift-corelibs-foundation,apple/swift-corelibs-foundation,e78l/swift-corelibs-foundation,apple/swift-corelibs-foundation,e78l/swift-corelibs-foundation,e78l/swift-corelibs-foundation,apple/swift-corelibs-foundation,e78l/swift-corelibs-foundation,apple/swift-corelibs-foundation,apple/swift-corelibs-foundation