Merge pull request #279 from MaikStohn/Marlin_v1

Fixed wrong code (will not even compile when EXTRUDERS>2)

Marlin/stepper.h

 
 #if EXTRUDERS > 2
   #define WRITE_E_STEP(v) { if(current_block->active_extruder == 2) { WRITE(E2_STEP_PIN, v); } else { if(current_block->active_extruder == 1) { WRITE(E1_STEP_PIN, v); } else { WRITE(E0_STEP_PIN, v); }}}
-  #define NORM_E_DIR() { if(current_block->active_extruder == 2) { WRITE(!E2_DIR_PIN, INVERT_E2_DIR); } else { if(current_block->active_extruder == 1) { WRITE(!E1_DIR_PIN, INVERT_E1_DIR); } else { WRITE(E0_DIR_PIN, !INVERT_E0_DIR); }}}
+  #define NORM_E_DIR() { if(current_block->active_extruder == 2) { WRITE(E2_DIR_PIN, !INVERT_E2_DIR); } else { if(current_block->active_extruder == 1) { WRITE(E1_DIR_PIN, !INVERT_E1_DIR); } else { WRITE(E0_DIR_PIN, !INVERT_E0_DIR); }}}
   #define REV_E_DIR() { if(current_block->active_extruder == 2) { WRITE(E2_DIR_PIN, INVERT_E2_DIR); } else { if(current_block->active_extruder == 1) { WRITE(E1_DIR_PIN, INVERT_E1_DIR); } else { WRITE(E0_DIR_PIN, INVERT_E0_DIR); }}}
 #elif EXTRUDERS > 1
   #define WRITE_E_STEP(v) { if(current_block->active_extruder == 1) { WRITE(E1_STEP_PIN, v); } else { WRITE(E0_STEP_PIN, v); }}