Bug 1635

here is a small bug in src/wifi/examples/wifi-phy-test.c
in line 126:  Simulator::Run ();
   line 127:  return m_output;
here needs   Simulator::Destroy();

and also 
in line 268:  Simulator::Run ();
   line 269:  return m_output;
here also needs Simulator::Destroy();

if we do not fix it, when run example :
./ns3.16-wifi-phy-test-debug  SizeVsRange 
here will be crashed , print error:
assert failed. cond="!m_state->IsStateTx () && !m_state->IsStateSwitching ()", file=../src/wifi/model/yans-wifi-phy.cc, line=507
terminate called without an active exception

so I debug code ,find that before a new simulation start, we should destroy the old simualtion.
And this bug still exist in current ns3-dev, not only ns-3.16