Allow Update and Draw functions to be turned off

allow nil to be passed as an argument to SetUpdateFunction and SetDrawFunction to turn off said functions.
Merge pull request #267 from sigatrev/Update-and-Draw

Allow Update and Draw functions to be turned off
Revert "replace psychopathic mapconv.exe with one compiled by "g++ (rev5, Built by MinGW-W64 project) 4.8.1""

This reverts commit 84a8d3adfb01a9905a24f1218263ec86ed2d6d6d.
Revert "Kyzentun: it's not your fault that our mapconv.exe is psychopathic"

This reverts commit 38aa07ce389a1cca1bada21d045072a9137b729e.