instant stop of sd prints from the panel.

Marlin/cardreader.pde

@@ -432,6 +432,7 @@ void CardReader::updir()
 
 void CardReader::printingHasFinished()
 {
+ quickStop();
  sdprinting = false;
  if(SD_FINISHED_STEPPERRELEASE)
  {

Marlin/stepper.cpp

@@ -752,3 +752,12 @@ void finishAndDisableSteppers()
   disable_z(); 
   disable_e(); 
 }
+
+void quickStop()
+{
+  DISABLE_STEPPER_DRIVER_INTERRUPT();
+  while(blocks_queued())
+    plan_discard_current_block();
+  ENABLE_STEPPER_DRIVER_INTERRUPT();
+}
+

Marlin/stepper.h

@@ -52,5 +52,5 @@ void finishAndDisableSteppers();
 
 extern block_t *current_block;  // A pointer to the block currently being traced
 
-
+void quickStop();
 #endif