Fix multiple stubs with different primitive args

This fixes the broken test case, but I'd like some feedback on how to do this better.  In particular, I'm not super comfortable with using typeid().  I'd prefer line 72 on StubbedMethod.mm to be:

if (Arguments::anything.get() == argument_ptr.get()) {

This doesn't work because Arguments::anything doesn't always return a shared pointer to the same Arguments::AnyArgument instance.  Shouldn't it do that since it's statically initialized (AnyArgument.h:24).