Critical M0/2/30 fix. Homing updates.

- Critical fix for M0 program pause. Due to its recent change, it would
cause Grbl to suspend but wouldn’t notify the user of why Grbl was not
doing anything. The state would show IDLE and a cycle start would
resume it. Grbl now enters a HOLD state to better indicate the state
change.

- Critical fix for M2 and M30 program end. As with M0, the state
previously would show IDLE while suspended. Grbl now does not suspend
upon program end and leaves job control to the GUI. Grbl simply reports
a `[Pgm End]` as a feedback message and resets certain g-code modes.

- M2/30 g-code reseting fix. Previously Grbl would soft-reset after an
M2/30, but this was not complaint to the (linuxcnc) g-code standard. It
simply resets [G1,G17,G90,G94,G40,G54,M5,M9,M48] and keeps all other
modes the same.

- M0/M2/M30 check-mode fix. It now does not suspend the machine during
check-mode.

- Minor bug fix related to commands similar to G90.1, but not G90.1,
not reporting an unsupported command.

- Homing cycle refactoring. To help reduce the chance of users
misunderstanding their limit switch wiring, Grbl only moves a short
distance for the locate cycles only. In addition, the homing cycle
pulls-off the limit switch by the pull-off distance to re-engage and
locate home. This should improve its accuracy.

- HOMING_FORCE_ORIGIN now sets the origin to the pull-off location,
rather than where the limit switch was triggered.

- Updated default junction deviation to 0.01mm. Recent tests showed
that this improves Grbl’s cornering behavior a bit.

- Added the ShapeOko3 defaults.

- Added new feedback message `[Pgm End]` for M2/30 notification.

- Limit pin reporting is now a $10 status report option. Requested by
OEMs to help simplify support troubleshooting.

grbl/gcode.c

@@ -219,7 +219,7 @@ uint8_t gc_execute_line(char *line)
               else { gc_block.modal.distance = DISTANCE_MODE_INCREMENTAL; } // G91
             } else {
               word_bit = MODAL_GROUP_G4;
-              if (mantissa != 10) { FAIL(STATUS_GCODE_UNSUPPORTED_COMMAND); } // [G90.1 not supported]
+              if ((mantissa != 10) || (int_value == 90)) { FAIL(STATUS_GCODE_UNSUPPORTED_COMMAND); } // [G90.1 not supported]
               mantissa = 0; // Set to zero to indicate valid non-integer G command.
               // Otherwise, arc IJK incremental mode is default. G91.1 does nothing.
             }
@@ -1028,18 +1028,41 @@ uint8_t gc_execute_line(char *line)
   // refill and can only be resumed by the cycle start run-time command.
   gc_state.modal.program_flow = gc_block.modal.program_flow;
   if (gc_state.modal.program_flow) { 
-    protocol_buffer_synchronize(); // Finish all remaining buffered motions. Program paused when complete.
-
-    sys.suspend = true;
-    protocol_execute_realtime(); // Suspend execution. For both program pause or program end.
-  
-    // If complete, reset to reload defaults (G92.2,G54,G17,G90,G94,M48,G40,M5,M9). Otherwise,
-    // re-enable program flow after pause complete, where cycle start will resume the program.
-    if (gc_state.modal.program_flow == PROGRAM_FLOW_COMPLETED) { mc_reset(); }
-    else { gc_state.modal.program_flow = PROGRAM_FLOW_RUNNING; } // Resume from program pause.
+	protocol_buffer_synchronize(); // Sync and finish all remaining buffered motions before moving on.
+	if (gc_state.modal.program_flow == PROGRAM_FLOW_PAUSED) {
+	  if (sys.state != STATE_CHECK_MODE) {
+		bit_true_atomic(sys.rt_exec_state, EXEC_FEED_HOLD); // Use feed hold for program pause.
+		protocol_execute_realtime(); // Execute suspend.
+	  }
+	} else { // == PROGRAM_FLOW_COMPLETED
+	  // Upon program complete, only a subset of g-codes reset to certain defaults, according to 
+	  // LinuxCNC's program end descriptions and testing. Only modal groups [G-code 1,2,3,5,7,12]
+	  // and [M-code 7,8,9] reset to [G1,G17,G90,G94,G40,G54,M5,M9,M48]. The remaining modal groups
+	  // [G-code 4,6,8,10,13,14,15] and [M-code 4,5,6] and the modal words [F,S,T,H] do not reset.
+	  gc_state.modal.motion = MOTION_MODE_LINEAR;
+	  gc_state.modal.plane_select = PLANE_SELECT_XY;
+	  gc_state.modal.distance = DISTANCE_MODE_ABSOLUTE;
+	  gc_state.modal.feed_rate = FEED_RATE_MODE_UNITS_PER_MIN;
+	  // gc_state.modal.cutter_comp = CUTTER_COMP_DISABLE; // Not supported.
+	  gc_state.modal.coord_select = 0; // G54
+	  gc_state.modal.spindle = SPINDLE_DISABLE;
+	  gc_state.modal.coolant = COOLANT_DISABLE;
+	  // gc_state.modal.override = OVERRIDE_DISABLE; // Not supported.
+	  
+	  // Execute coordinate change and spindle/coolant stop.
+	  if (sys.state != STATE_CHECK_MODE) {
+		if (!(settings_read_coord_data(gc_state.modal.coord_select,coordinate_data))) { FAIL(STATUS_SETTING_READ_FAIL); } 
+		memcpy(gc_state.coord_system,coordinate_data,sizeof(coordinate_data));
+		spindle_stop();
+		coolant_stop();		
+	  }
+	  
+	  report_feedback_message(MESSAGE_PROGRAM_END);
+	}
+    gc_state.modal.program_flow = PROGRAM_FLOW_RUNNING; // Reset program flow.
   }
     
-  // TODO: % to denote start of program. Sets auto cycle start?
+  // TODO: % to denote start of program.
   return(STATUS_OK);
 }