more fixes in 'tests/crypto/GNUmakefile' (build failures on RHEL6 and NetBSD):
- -lboost_thread$(BOOST_LIBRARY_TAG) is a required library by -lboost_filesystem
  (transitive dependency)
- LD_LIBRARY_PATH must contain $(BOOST_LIB_DIR) in order to find the boost libraries
  when running the tests