Bug 1042824 - Do a security check on the callee in ExportFunction. r=gabor

It would be nice to enforce this in New*FunctionForwarder, but we're already
in the target compartment at that point. :-(

We don't need to worry about this at the other callsites of
New*FunctionForwarder because:
* The stuff in XPCComponents is always invoked by System Principaled code.
* The stuff in StackScopedCloneRead only gets invoked when we're already done a
  successful CheckedUnwrap inside the JS engine.
Bug 1042824 - Manually do the cross-compartment call in NonCloningFunctionForwarder. r=gabor
Bug 1042824 - Borrow the JSID_VOID handling from the cloning forwarding. r=gabor
Bug 1042824 - Remove implicit cloning behavior in function forwarders. r=gabor
Bug 1042840 - Remove evalInWindow. r=gabor