(svn r4486) - NewGRF: Create and use a memory pool to manage sprite groups. This
reduces the amount of house keeping we do and the chance of memory
leaks.

(svn r3077) static, const, bracing, indentation, 0 -> '\0'/NULL, typos in comments, excess empty lines, minor other changes
nothing spectacular, just some stuff, which piled up

(svn r2962) - const correctness for all Get* functions and most Draw* functions that don't change their pointer parameters
- change a lot of byte player types to PlayerID
- beautify header files, same "#endif /* filename */" ending

(svn r2389) - Feature: [newgrf] Implement the mechanism for handling newgrf callbacks.
- Feature: [newgrf] Implement the 'refit capacity' callback.