Small Modifications

This is my first pull request, I hope that I am participating in a reasonable fashion.

The s_thread_shim function in zactor.c has inconsistent variable name usage that I fixed to look like the other functions around it.

The other two fixes that I made were geared towards Windows. I'm working with MinGW-w64 and MSYS. I added a couple of conditional compile statements to make Windows happy with some printf statements using the %zd format which Windows does not understand. Also modified a conditional compile statement to be used for both MSC and MINGW32.

Thanks,
Dan Riegsecker