It passes all tests when run serialized, but still gives weird errors
(OperationalError: database is locked) when run with -j5. sqlite3 shouldn't
be barfing just because the database is locked, since the default timeout is
5 seconds, and it's dying *way* faster than that.
We had a bug (fixed in the previous commit) where doing 'redo-ifchange
dirname' (which runs dirname/all.do) would not create the stamp correctly,
so that it would always show up as dirty.
It's a little bit complicated to simulate, but this does it.
Unfortunately it failed before the previous patch, so that's why this test
is needed :(
The test is a little ugly, because the bug I'm testing for didn't happen
except if you ran 'redo' two times in a row, not two times inside the same
redo session. That's because dependency caching inside the one session
prevents the accidental rebuild.
