Added AddInputCallback and RemoveInputCallback to Lua API for screen.  ScreenManager now passes input to the lua side of each screen in addition to the engine side.
explain what this repo is about, compared to mainline
it's very important to note that this branch is not mainline. [nomerge]
= Operator should check for self-assignment
Minor performance enhancement

`list.empty()` runs in constant time; `list.size` can run in linear time.
`list.empty()` runs in constant time; `list.size` can run in linear time.

Sources:
http://www.cplusplus.com/reference/list/list/size/
http://www.cplusplus.com/reference/list/list/empty/
Remove memory leak in RageSurfaceUtils::Palettize
Merge branch 'patch-2' of https://github.com/moshekaplan/stepmania
Merge branch 'patch-3' of https://github.com/moshekaplan/stepmania
Added semicolon that moshekaplan forgot.
Merge pull request #206 from kyzentun/InputCallbacks

This seems solid in my testing, I've converted Consensual to use it instead of CodeMessageCommand.
Added Actor:GetDestX/Y/Z to Lua API.
Merge branch 'master' of github.com:stepmania/stepmania