properly clean up state in wiringXGC()
properly clean up state in wiringXGC()

In case somebody gets the idea to run wiringXGC() multiple times,
the call to platform->gc() will happen on free'd memory!
Also unset issetup so any later call to wiringXSetup can succeed.

wiringX/wiringX,wiringX/wiringX,mxOBS/wiringX,mxOBS/wiringX,mxOBS/wiringX,wiringX/wiringX