Now t/curse passes again when parallelized (except for the countall
mismatch, since we haven't fixed the source of that problem yet). At least
it's consistent now.
There's a bunch of stuff rearranged in here, but the actual important
problem was that we were doing unlink() on the lock fifo even if ENXIO,
which meant a reader could connect in between ENXIO and unlink(), and thus
never get notified of the disconnection. This would cause the build to
randomly freeze.
...because it seems my locking isn't very good. It exposes annoying
problems involving rebuilding the same files more than once, screwing up
stamp files with redo -j, and being unnecessarily slow when checking
dependencies. So it's a pretty good test considering how simple it is.
Didn't add it to t/all.do yet, because it would fail.
