Forward non-signal binding invocations to QObject::qt_metcall()

Check the methodId in QtSignalForwarder, if it isn't from the range
allocated for signal bindings, forward it to the standard
QObject::qt_metacall() implementation.
Fix VS2010 build

std::function does not allow discarding return values in VS2010
as explained at
http://stackoverflow.com/questions/6628442/can-tr1function-swallow-return-values