Quickly hack together exception testing based on the lightweight test header.
There are several compilers which Boost.Test doesn't work on and I'd like to
run the exception tests on them. But having said that, Boost.Test offers much
that this doesn't so I'm implementing it so that, hopefully, compilers which
can use Boost.Test can be switched back in the future.
But this needs more testing before I add it to the boost trunk.