Search for both release and debug library variants, and use
SelectLibraryConfigurations to choose the appropriate
library. Also add both release and debug libraries to the
imported targets.
- autodetects Ice on all major platforms
- allows building with all supported Visual Studio versions on Windows
- autodetects the slice path on most platforms
- separately detects the Ice programs, headers, slice files and
libraries so that any Ice configuration or installation errors can
be accurately reported, making diagnosis of Ice problems simpler
