LCD home button causes repeated homing (PR#175)

Fix: increased debounce delay.

Marlin/Marlin_main.cpp

     // Check to see if we have to home, use poor man's debouncer
     // ---------------------------------------------------------
     static int homeDebounceCount = 0;   // poor man's debouncing count
-    const int HOME_DEBOUNCE_DELAY = 750;
+    const int HOME_DEBOUNCE_DELAY = 2500;
     if (!READ(HOME_PIN)) {
       if (!homeDebounceCount) {
         enqueuecommands_P(PSTR("G28"));