Fix zcurve.c so it builds on Windows
 * Don't include platform.h when building using Visual Studio
 * umask doesn't work the way it was used here, so just don't call
   it on Windows
 * Make sure to cast void * to the type you're assigning it to on Windows
Changes nothing, just rearranges the sections as visual studio likes
Add RelWithDebInfo configuration

 * This builds the Release DLL and also Debug info pdb files
 * Debug info is no longer built for the ReleaseDLL configuration
Change so we only don't include platform.h when using visual studio, but do otherwise
Make build directory for Win32 RelWitDebInfo $(PlatformName)\$(ConfigurationName)
Add zcurve.[ch] to the czmq project
Merge pull request #169 from vortechs2000/more_windows_fixes

More windows fixes