[DotGNU]csunit moved to pnet

[Rhys Weatherley]

I have moved the source for the "csunit" program from pnetlib
to pnet so that we can eventually reuse the test framework
for other libraries and applications.  It is now installed
as part of the pnet development toolchain.

I will be removing the copy in pnetlib and updating pnetlib's
build system once we nail down what the new directory layout
and build scripts will look like.

Cheers,

Rhys.