Fix MSVC compiling warnings and remove an unused texture

I know, I should make two pull requests for two diffrent things but I couldn't find a better title for it.

The string "ladder_down(.png)" was contain in any file, so it's not used anymore.
And the two removed lines solve about 10 type C4351 warnings. (See http://msdn.microsoft.com/en-us/library/1ywe7hcy(v=vs.100).aspx )

Tested on Windows XP.