[Mark McLeod]

Something such as:

  static char toggle=1;

  if(p4_sw_trig && toggle)
  {
	toggle = 0;
  	relay2_fwd = !relay2_fwd; 
  	relay2_rev = 0;
  }
  if(!p4_sw_trig)
  {
	toggle = 1;
  }

prevents further toggling until the button has been released again.