Spindle enable pin with variable spindle option fix.

- [fix] When USE_SPINDLE_DIR_AS_ENABLE_PIN is enabled in config.h, the
enable pin was not being set when spindle speed is zero. This behavior
should now be fixed.

grbl/grbl.h

@@ -23,7 +23,7 @@
 
 // Grbl versioning system
 #define GRBL_VERSION "1.1e"
-#define GRBL_VERSION_BUILD "20161219"
+#define GRBL_VERSION_BUILD "20170103"
 
 // Define standard libraries used by Grbl.
 #include <avr/io.h>

grbl/spindle_control.c

@@ -115,19 +115,11 @@ void spindle_stop()
   // and stepper ISR. Keep routine small and efficient.
   void spindle_set_speed(uint8_t pwm_value)
   {
+    SPINDLE_OCR_REGISTER = pwm_value; // Set PWM output level.
     if (pwm_value == SPINDLE_PWM_OFF_VALUE) {
-      spindle_stop();
+      SPINDLE_TCCRA_REGISTER &= ~(1<<SPINDLE_COMB_BIT); // Disable PWM. Output voltage is zero.
     } else {
-      SPINDLE_OCR_REGISTER = pwm_value; // Set PWM output level.
       SPINDLE_TCCRA_REGISTER |= (1<<SPINDLE_COMB_BIT); // Ensure PWM output is enabled.
-
-      #if defined(USE_SPINDLE_DIR_AS_ENABLE_PIN)
-        #ifdef INVERT_SPINDLE_ENABLE_PIN
-          SPINDLE_ENABLE_PORT &= ~(1<<SPINDLE_ENABLE_BIT);
-        #else
-          SPINDLE_ENABLE_PORT |= (1<<SPINDLE_ENABLE_BIT);
-        #endif
-      #endif
     }
   }
 
@@ -194,7 +186,8 @@ void spindle_stop()
         if (state == SPINDLE_ENABLE_CCW) { rpm = 0.0; } // TODO: May need to be rpm_min*(100/MAX_SPINDLE_SPEED_OVERRIDE);
       }
       spindle_set_speed(spindle_compute_pwm_value(rpm));
-    #else
+    #endif
+    #if defined(USE_SPINDLE_DIR_AS_ENABLE_PIN) || !defined(VARIABLE_SPINDLE)
       // NOTE: Without variable spindle, the enable bit should just turn on or off, regardless
       // if the spindle speed value is zero, as its ignored anyhow.
       #ifdef INVERT_SPINDLE_ENABLE_PIN