Made "stop heating wait" optional.

Default off.

Marlin/Configuration.h

 // Heating is finished if a temperature close to this degree shift is reached
 #define HEATING_EARLY_FINISH_DEG_OFFSET 1 //Degree
 
+//Do not wait for M109 to finish when printing from SD card
+//#define STOP_HEATING_WAIT_WHEN_SD_PRINTING
+
 // PID settings:
 // Uncomment the following line to enable PID support.
 #define PIDTEMP

Marlin/cardreader.pde

  st_synchronize();
  quickStop();
  sdprinting = false;
+ #ifdef STOP_HEATING_WAIT_FOR_SD_PRINTING
  stop_heating_wait=true;
+ #endif
  if(SD_FINISHED_STEPPERRELEASE)
  {
    //finishAndDisableSteppers();