Fix windows builds

The vcproj changes aren't quite as horrific as they look if you don't show the whitespace changes.

* Only define true/false and typedef char bool on Windows when no building using
  C++ and true isn't defined.  On all other platforms just use stdbool.h.
* create a typedef for mode_t when on Windows
* Only include platform.h on non-Windows platforms
* Explicitly cast return type from mallocs - czmq is built with the C++ compiler
  on windows, so this is required.
* Add zfile.c and zsys.c to the czmq vcproj definition
* Add Ws2_32.lib and Iphlpapi.lib to the czmq_selftest.vcproj dependencies list;
  these are needed for socket-type operations.