Limit Switch locations based on MIN/MAX limits and homing direction

fixes #246
Added statements to set the limit switch positions to the maximum travel if homing in the positive direction as well as bed center at (0,0) if defined.
Relocated code based on feedback.

Marlin/Configuration_adv.h

@@ -76,6 +76,54 @@
 
 #define ENDSTOPS_ONLY_FOR_HOMING // If defined the endstops will only be used for homing
 
+
+//// AUTOSET LOCATIONS OF LIMIT SWITCHES
+//// Added by ZetaPhoenix 09-15-2012
+#ifdef MANUAL_HOME_POSITION  //Use manual limit switch locations
+  #define X_HOME_POS MANUAL_X_HOME_POS
+  #define Y_HOME_POS MANUAL_Y_HOME_POS
+  #define Z_HOME_POS MANUAL_Z_HOME_POS
+#else //Set min/max homing switch positions based upon homing direction and min/max travel limits
+  //X axis
+  #if X_HOME_DIR == -1
+    #ifdef BED_CENTER_AT_0_0
+      #define X_HOME_POS X_MAX_LENGTH * -0.5
+    #else
+      #define X_HOME_POS X_MIN_POS
+    #endif //BED_CENTER_AT_0_0
+  #else    
+    #ifdef BED_CENTER_AT_0_0
+      #define X_HOME_POS X_MAX_LENGTH * 0.5
+    #else
+      #define X_HOME_POS X_MAX_POS
+    #endif //BED_CENTER_AT_0_0
+  #endif //X_HOME_DIR == -1
+  
+  //Y axis
+  #if Y_HOME_DIR == -1
+    #ifdef BED_CENTER_AT_0_0
+      #define Y_HOME_POS Y_MAX_LENGTH * -0.5
+    #else
+      #define Y_HOME_POS Y_MIN_POS
+    #endif //BED_CENTER_AT_0_0
+  #else    
+    #ifdef BED_CENTER_AT_0_0
+      #define Y_HOME_POS Y_MAX_LENGTH * 0.5
+    #else
+      #define Y_HOME_POS Y_MAX_POS
+    #endif //BED_CENTER_AT_0_0
+  #endif //Y_HOME_DIR == -1
+  
+  // Z axis
+  #if Z_HOME_DIR == -1 //BED_CENTER_AT_0_0 not used
+    #define Z_HOME_POS Z_MIN_POS
+  #else    
+    #define Z_HOME_POS Z_MAX_POS
+  #endif //Z_HOME_DIR == -1
+#endif //End auto min/max positions
+//END AUTOSET LOCATIONS OF LIMIT SWITCHES -ZP
+
+
 //#define Z_LATE_ENABLE // Enable Z the last moment. Needed if your Z driver overheats.
 
 // A single Z stepper driver is usually used to drive 2 stepper motors.