Fix the commandblock's check for quiting the formspec

The submit button also sends a quit field.
Merge pull request #168 from ShadowNinja/fix-commandblock-quit

Fix the commandblock's check for quiting the formspec
use one ABM for blinkyplant instead of two.

using two ABMs allows the engine to desynchronize them, which makes the
duty cycle unpredictable.
use the right mesecon:receptor_* call for on/off blinkyplant
Improve the LuaController

Changes:
  * Stops code after a certain number of instructions.
  * Allows functions, due to instruction counting.
  * Allows loops and goto with non-JIT Lua (LuaJIT doesn't count looping as an instruction, allowing infinite loops), due to instruction counting.
  * Removes string matching functions as they can be slow.
  * Adds some safe functions.
  * Limits the amount of printing that can be done (to prevent console flooding).
  * Code cleanup.
  * More...