Replace extrudemultiply by extruder_multiply[active_extruder]

Fix for #1460.

Seems to work with only one extruder. Can't test this myself with more.

Marlin/Marlin.h

 extern float homing_feedrate[];
 extern bool axis_relative_modes[];
 extern int feedmultiply;
-extern int extrudemultiply; // Sets extrude multiply factor (in percent) for all extruders
 extern bool volumetric_enabled;
 extern int extruder_multiply[EXTRUDERS]; // sets extrude multiply factor (in percent) for each extruder individually
 extern float filament_size[EXTRUDERS]; // cross-sectional area of filament (in millimeters), typically around 1.75 or 2.85, 0 disables the volumetric calculations for the extruder.

Marlin/Marlin_main.cpp

 bool axis_relative_modes[] = AXIS_RELATIVE_MODES;
 int feedmultiply = 100; //100->1 200->2
 int saved_feedmultiply;
-int extrudemultiply = 100; //100->1 200->2
 int extruder_multiply[EXTRUDERS] = ARRAY_BY_EXTRUDERS(100, 100, 100, 100);
 bool volumetric_enabled = false;
 float filament_size[EXTRUDERS] = ARRAY_BY_EXTRUDERS(DEFAULT_NOMINAL_FILAMENT_DIA, DEFAULT_NOMINAL_FILAMENT_DIA, DEFAULT_NOMINAL_FILAMENT_DIA, DEFAULT_NOMINAL_FILAMENT_DIA);
       extruder_multiply[tmp_extruder] = sval;
     }
     else {
-      extrudemultiply = sval;
+      extruder_multiply[active_extruder] = sval;
     }
   }
 }
     //SERIAL_PROTOCOLPGM("Filament dia (measured mm):");
     //SERIAL_PROTOCOL(filament_width_meas);
     //SERIAL_PROTOCOLPGM("Extrusion ratio(%):");
-    //SERIAL_PROTOCOL(extrudemultiply);
+    //SERIAL_PROTOCOL(extruder_multiply[active_extruder]);
   }
 
   /**

Marlin/dogm_lcd_implementation.h

       lcd_printPGM(PSTR("dia:"));
       lcd_print(ftostr12ns(filament_width_meas));
       lcd_printPGM(PSTR(" factor:"));
-      lcd_print(itostr3(extrudemultiply));
+      lcd_print(itostr3(extruder_multiply[active_extruder]));
       lcd_print('%');
     }
   #endif

Marlin/planner.cpp

   block->steps[Z_AXIS] = labs(dz);
   block->steps[E_AXIS] = labs(de);
   block->steps[E_AXIS] *= volumetric_multiplier[active_extruder];
-  block->steps[E_AXIS] *= extrudemultiply;
+  block->steps[E_AXIS] *= extruder_multiply[active_extruder];
   block->steps[E_AXIS] /= 100;
   block->step_event_count = max(block->steps[X_AXIS], max(block->steps[Y_AXIS], max(block->steps[Z_AXIS], block->steps[E_AXIS])));
 
     delta_mm[Y_AXIS] = dy / axis_steps_per_unit[Y_AXIS];
   #endif
   delta_mm[Z_AXIS] = dz / axis_steps_per_unit[Z_AXIS];
-  delta_mm[E_AXIS] = (de / axis_steps_per_unit[E_AXIS]) * volumetric_multiplier[active_extruder] * extrudemultiply / 100.0;
+  delta_mm[E_AXIS] = (de / axis_steps_per_unit[E_AXIS]) * volumetric_multiplier[active_extruder] * extruder_multiply[active_extruder] / 100.0;
 
   if (block->steps[X_AXIS] <= dropsegments && block->steps[Y_AXIS] <= dropsegments && block->steps[Z_AXIS] <= dropsegments) {
     block->millimeters = fabs(delta_mm[E_AXIS]);

Marlin/ultralcd.cpp

     MENU_MULTIPLIER_ITEM_EDIT(int3, MSG_BED, &target_temperature_bed, 0, BED_MAXTEMP - 15);
   #endif
   MENU_MULTIPLIER_ITEM_EDIT(int3, MSG_FAN_SPEED, &fanSpeed, 0, 255);
-  MENU_ITEM_EDIT(int3, MSG_FLOW, &extrudemultiply, 10, 999);
+  MENU_ITEM_EDIT(int3, MSG_FLOW, &extruder_multiply[active_extruder], 10, 999);
   MENU_ITEM_EDIT(int3, MSG_FLOW MSG_F0, &extruder_multiply[0], 10, 999);
   #if TEMP_SENSOR_1 != 0
     MENU_ITEM_EDIT(int3, MSG_FLOW MSG_F1, &extruder_multiply[1], 10, 999);