Variadic when now does not cast result values

This fixes a memory management issue I had when developing an app. I was not able to run the tests. I did verify that it now works in my app.

Test error: `Test target PromiseKitTests encountered an error (Test session exited(1) without checking in.`

    2014-12-11 09:50:43.167 Beginning test session with Xcode 6A2006
    2014-12-11 09:50:43.167 Testing on device: <DVTiPhoneSimulator: 0x7f89f77a10d0> {
                    SimDevice: SimDevice : iPad 2 (E89774AF-2413-49D4-9D56-E3E9D04AD16A) : state={ Booted } deviceType={ SimDeviceType : com.apple.CoreSimulator.SimDeviceType.iPad-2 } runtime={ SimRuntime : 8.1 (12B411) - com.apple.CoreSimulator.SimRuntime.iOS-8-1 }
    }
    2014-12-11 09:50:43.167 Initializing test infrastructure.
    2014-12-11 09:50:43.167 Writing testing status log to /var/folders/cs/7648cd414f1bzz2r31dtgp200000gn/T/com.apple.dt.XCTest-status/Session-2014-12-11_09:50:43-1pvAej.log.
    2014-12-11 09:50:43.206 Creating the connection.
    2014-12-11 09:50:43.206 Listening for proxy connection request from the test bundle (all platforms)
    2014-12-11 09:50:43.206 Resuming the connection.
    2014-12-11 09:50:43.206 Test connection requires daemon assistance.
    2014-12-11 09:50:43.210 Checking test manager availability..., will wait up to 120s
    2014-12-11 09:50:43.211 testmanagerd handled session request.
    2014-12-11 09:50:43.211 Waiting for test process to launch.
    2014-12-11 09:50:45.883 Launch session started, setting a disallow-finish-token on the run operation.
    2014-12-11 09:50:45.887 Waiting for test process to check in..., will wait up to 120s
    2014-12-11 09:50:45.910 Adding console adaptor for test process.

    **** Begin output from test process:
    2014-12-11 09:50:47.643 xctest[38941:17111316] The test bundle at /Users/jeroen/Code/PromiseKit/swift/Build/Products/Debug-iphonesimulator/PromiseKitTests.xctest could not be loaded because an unanticipated error occurred.
    2014-12-11 09:50:47.644 xctest[38941:17111316] Detailed error information: Error Domain=NSCocoaErrorDomain Code=3587 "The bundle “PromiseKitTests” couldn’t be loaded because it is damaged or missing necessary resources." (dlopen_preflight(/Users/jeroen/Code/PromiseKit/swift/Build/Products/Debug-iphonesimulator/PromiseKitTests.xctest/PromiseKitTests): Library not loaded: @rpath/libswiftAssetsLibrary.dylib
      Referenced from: /Users/jeroen/Code/PromiseKit/swift/Build/Products/Debug-iphonesimulator/PromiseKit.framework/PromiseKit
      Reason: image not found) UserInfo=0x7a829ef0 {NSLocalizedRecoverySuggestion=Try reinstalling the bundle., NSFilePath=/Users/jeroen/Code/PromiseKit/swift/Build/Products/Debug-iphonesimulator/PromiseKitTests.xctest/PromiseKitTests, NSLocalizedFailureReason=The bundle is damaged or missing necessary resources., NSLocalizedDescription=The bundle “PromiseKitTests” couldn’t be loaded because it is damaged or missing necessary resources., NSDebugDescription=dlopen_preflight(/Users/jeroen/Code/PromiseKit/swift/Build/Products/Debug-iphonesimulator/PromiseKitTests.xctest/PromiseKitTests): Library not loaded: @rpath/libswiftAssetsLibrary.dylib
      Referenced from: /Users/jeroen/Code/PromiseKit/swift/Build/Products/Debug-iphonesimulator/PromiseKit.framework/PromiseKit
      Reason: image not found, NSBundlePath=/Users/jeroen/Code/PromiseKit/swift/Build/Products/Debug-iphonesimulator/PromiseKitTests.xctest}
    **** End output from test process

    2014-12-11 09:50:49.804 Test operation failure: Test session exited(1) without checking in.
    2014-12-11 09:50:49.804 _finishWithError:Error Domain=IDEUnitTestsOperationsObserverErrorDomain Code=3 "Test session exited(1) without checking in." UserInfo=0x7f89f867e830 {NSLocalizedDescription=Test session exited(1) without checking in.} didCancel: 1