[crossfire] Merged WIN32/Unix code

[Andreas Kirschbaum]

I've just committed some code that merges a big

    #ifdef WIN32
        ...
    #else
        ...
    #endif

block which was quite similar for both the windows and the non-windows
parts. (Nevertheless it did contain different bugs/applied bug fixes...)

It does work on Linux, but it probably breaks windows compilation as I
do not have access to a windows compiler. At least
PLUGIN_SUFFIX=\".dll\" is missing from the windows build system now.