Fixed homing fail alarm handling. Re-integrated software debouncing.

- [bug] Fixed a homing fail issue, where the alarm was not being set
right, not cleared correctly. It would report the wrong code and enter
an infinite alarm loop. This was due to how alarm codes were altered a
while back. Now updated and fixed to show the right codes.

- [feature] Re-installed optional software debouncing for hard limit
switches. By request.

grbl/config.h

@@ -454,6 +454,15 @@
 // #define RX_BUFFER_SIZE 128 // (1-254) Uncomment to override defaults in serial.h
 // #define TX_BUFFER_SIZE 100 // (1-254)
 
+// A simple software debouncing feature for hard limit switches. When enabled, the interrupt 
+// monitoring the hard limit switch pins will enable the Arduino's watchdog timer to re-check 
+// the limit pin state after a delay of about 32msec. This can help with CNC machines with 
+// problematic false triggering of their hard limit switches, but it WILL NOT fix issues with 
+// electrical interference on the signal cables from external sources. It's recommended to first
+// use shielded signal cables with their shielding connected to ground (old USB/computer cables 
+// work well and are cheap to find) and wire in a low-pass circuit into each limit pin.
+// #define ENABLE_SOFTWARE_DEBOUNCE // Default disabled. Uncomment to enable.
+
 // Configures the position after a probing cycle during Grbl's check mode. Disabled sets
 // the position to the probe target, when enabled sets the position to the start position.
 // #define SET_CHECK_MODE_PROBE_TO_START // Default disabled. Uncomment to enable.