Add CppCheck file.

[CppCheck](http://cppcheck.sourceforge.net/) is an Open Source static analysis tool.

I sometimes use it to check that I haven't completely broken the game in some obvious way. 
Perhaps if I'd done this we wouldn't have had the recent issues caused by my OpenGL 3.x work.

Here is the configuration file that I use in case anyone else wants to try it out or add too it.

Andy