Fix most of clipboard-related memory leaks and potential crashes; Fixes jacob#23
fix sim.deleteStamp and sim.loadStamp (couldn't load/delete stamps with names like 530e908700)
fix numpad behavior: movement keys are no longer triggered with numlock on
fix error logging in lua key events
Fix Lua API sim.partNeighbours with 4 arguments
Fix bug in Lua API sim.neighbours() causing some particles to be missed out

Was excluding all particles with the same x or y as the centre instead of just the centre particle.
Do not use loadstring to load autorun (who even wrote this?). Also print a message in case of successful autorun load
Fix more bugs in the Lua API

Crash with sim.partKill(large number).
sim.neighbours() looking for particles in completely the wrong place.
Impossible to tell from sim.partID whether a particle exists, since it returns 0 both if there is no particle there and if particle 0 is there.
lots of random fixes to the legacy lua api
Merge branch 'develop' of https://github.com/simtr/The-Powder-Toy into develop