Added 2nd extruder temperature LCD readout and setting.

adding M120 and 121 for turning on and off the endstops only for homing

Fix to allow M120/M121

Fix compile error on boards without a bed heater.

I could not find why this problem was introduced. 
Its quite obvious, so I think its in general interest to merge.

Wrap the call to turn off the bed heater in a #if to prevent a compile error on boards that do not have a bed heater

reinitialize the lcd, if the SD card is inserted or removed. It seems that LCDs can confused by electrical discharges from time to time.
Since a removal or insert of the sd card takes a long time in firmware, just reinitializing the lcd does not hurt.
actually, it solves a problem with the UltiControlle

see https://github.com/ErikZalm/Marlin/issues/148

make should rebuild if configuration or Makefile is changed

Changed SLOWDOWN. IF this does not work ok OLD_SLOWDOWN is the old algo.

Fix for wrong systax in #ifdef.

This breaks temperature readout for pronterface!

- Fixed a typo

Fixed small bug in arcs
M105 prints now actual_temp/target_temp

Moved the PID_dT in the Ki and Kd calculation from the configuration.h to temperature.cpp

For upstream

Fix compilation error when PIDTEMP is undefined and ULTIPANEL is defined...