[Build-Win32] dllmap is not supported by the MS .NET impl

The MS .NET framework will throw a
System.Configuration.ConfigurationErrorsException, dllmaps are a mono
extension and absolutely not portable.
For coding, the msbuild-preprocess.ps1 now copies recommended configs for
Win32 located inside 'lib/win32'.
After that smuxi-frontend-gnome.exe and smuxi-server.exe work out of the
box if compiled with Visual Studio.