windows: Make windows/main.c independent from unix/main.c

Up to know changes unix/main.c were able to break the windows
build because windows/main.c simply included unix/main.c.

Now windows/main.c stands on it's own and won't break if
unix/main.c changes.
Merge pull request #240 from msiemens/windows_fix

windows: Make windows/main.c independent from unix/main.c