Merge pull request #152 from loganb/Marlin_v1

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.
Added support for 2nd extruder temperature to UltraLCD
Show proper temperature for extruder 2
adding M120 and 121 for turning on and off the endstops only for homing function
Fix to allow M120/M121
Merge pull request #156 from Atntias/patch-2

Fix to allow M120/M121
Merge pull request #155 from Atntias/patch-1

adding M120 and 121 for turning on and off the endstops only for homing
Merge pull request #154 from daid/Marlin_v1

Added 2nd extruder temperature LCD readout and setting.
Added temperature window to M109. This is needed for systems with no overshoot PID.
Merge branch 'Marlin_v1' of github.com:ErikZalm/Marlin into Marlin_v1
Small cleanup
Added option to increase the FAN PWM frequency.
fixed typo in comment
delete obsolete and wrong code

"i" runs from 0 to 4 but "add_homeing" array size is 3 only. On the
other hand the calculated value gets overwritten by either one of the
if choice.
explicit includes to make it compile with AVRStudio/Eclipse
Moved LCD initialization out of constructor

Since the class "MainMenu" was used within a static variable the
initialization of the object (constructor call) was done before Arduino
library startup. It always caused a crash when using AVRStudio with
JTAG debugger (caused from calling the LCD initialization / the lot of
I/O work / the stack used during this calls). By moving the LCD_INIT
out of the constructor and using an explicit call inside of Arduino
setup() implementation immediately fixed all problems and the JTAG
debugger runs fine.
magic PROGMEM defines to avoid hundreds of wrong GCC warnings
added missing declaration of buttons_init()

This is required when moving the buttons_init() function to the
lcd_init() function
futher docu of M500
Revert "magic PROGMEM defines to avoid hundreds of wrong GCC warnings"

This reverts commit 3682d9bd5b34bdc6560d97278d6d7eff3243bddc.