ifdef FLC rendering placement (should fix bug #294)

This uses old centering code for Windows, otherwise uses new centering code.
I use the same options under Linux as in bug report #294.
The centering code that works on one seems to have problems on the other.
Used for fixing:
  #ifdef _WIN32
    ...
  #else
    ...
  #endif

These issues may be system and/or SDL version dependent.
More bug reports may be needed to work this out.