Make a couple of selftests clean up a bit better

1. in src/1 it generates a scratchTheory, but did not remove the .dat
file
2. in tools/Holmake/tests/coproduct it does not clean testdir2 before
starting, allowing for stale/unhelpful Moscow ML dependency info to
linger there.

Fix a bug in generation of dependencies for Holmake "side products"

Slightly extend test-cases

Test more Holmake/coproduct scenarios

Include doing it all entirely with -j1

Add file omitted from previous commit