This time, I tweaked usability a bit, as far as lock contention goes. People running dpb regularly knows dpb locks the host during depends/prepare/prepare-results/junk.
Now, that locking is more explicit: dpb tries to obtain the lock, and if it can't it will create a separate task that waits for the lock. So that makes for a better display, since one can distinguish between a depends taking a lot of time, and waiting-for-lock. (plus I can count how many locks I've been waiting for, so the actual display is more: some/pkgpath(waiting for lock #25) unchanged for 68 seconds rather than something less explicit.
