Windows compliation fixes

[Neil Mitchell]

Hi

worldmap/level_dot.cxx
This requires the sqrt function, which is defined in math.h, so math.h needs
to be included in this file, or one of the files included by it. As far as I
can see the logical place is in the file. I'm not sure if this should be
included in the linux version as well or not.

system.cxx, System::get_language()
Pingus\src\system.cxx(346) : error C2065: 'LC_MESSAGES' : undeclared
identifier
No idea what this code does exactly, but MSDN doesn't seem to know anything
about LC_MESSAGES. Can this code be ifdef'd and reverted to how it was for
Windows, or is there a better fix?

Neil