OS X build support

Hello Vasiliy, I added a quick and dirty fix for OS X build and crash that I experienced in the menu. It needs to be properly fixed and cleaned, but I had spent a lot of time on just getting it to compile, so I wanted to run it ASAP.

I experience a lot of different crashes and bugs (e.g. menu widgets are broken, cannot shoot, physics related crash in Survivor, etc.), do you think it is something you could have introduced or was it like that from the start when the source code was released by Frozenbyte?

Thanks for the work you've done.