Because the TTY hooks interface was not finished when I imported the
MPSAFE TTY layer, I had to disconnect the snp(4) driver. This snp(4)
implementation has been sitting in my P4 branch for some time now.
Unfortunately it still doesn't use the same error handling as snp(4)
(returning codes through FIONREAD), but it should already be usable.
I'm committing this to SVN, hoping someone else could polish off its
rough edges. It's always better than having a broken driver sitting in
the tree.
