FindBoost: Output Boost_LIB_PREFIX if Boost_DEBUG=ON requested
Output Boost_NAMESPACE too.
This is helpful when troubleshooting Boost look-up failure eg. due to missing set(Boost_USE_STATIC_LIBS ON)
in case user's environment does not have shared Boost libraries deployed.
Topic-rename: FindBoost-debug-lib-prefix
Edited by Brad King