[Toybox] mkroot works again, pending release.

[Rob Landley]

I got toysh implementing all the bits that mkroot's init script needs, so I
expect to cut a release in the next couple days. There's still a zillion
dangling threads but I should be able to park it for now.

If anybody wants to holler about something I should fix now, this would be a
good time. I'm back in tokyo working on $DAYJOB again, and am likely to down
tools on toybox after the release for at least a couple months.

I note that except for a couple large holes (lack of $((math)) and function()
support, haven't finished trap/signal/jobs, needs command line editing and
history) toysh is... sort of working now? Several known bugs (test suite
failures), but it's actually starting to be actually run real scripts. Needs
auditing for memory leaks, and the largest script I've thrown at it _is_ the
mkroot init, but... it's advanced from "don't bother" to "object of curiosity".

Right now, useful bug reports would come in the form of "thing I could add to
tests/sh.test and get to later", and keep in mind I've got...

  $ wc sh.tests
  845  3791 20673 sh.tests

One or two of those already, not yet properly formatted into runnable regression
tests. (And one of the current sh.test entries HANGS because a
subshell-plus-redirection test fails to hand off a filehandle properly and we
wait forever reading from nothing, so I need to teach tests to time out...)

Rob