script/lei: handle SIGTSTP and SIGCONT

script/lei: handle SIGTSTP and SIGCONT

Sometimes it's useful to pause an expensive query or
refresh-mail-sync to do something else.  While lei-daemon and
lei/store can't be paused since they're shared across clients,
per-invocation WQ workers can be paused safely using the
unblockable SIGSTOP.

While we're at it, drop the ETOOMANYREFS hint since it
hasn't been a problem since we drastically reduced FD passing
early in development.