Parse & merge Postgres connect strings
configure.ac: check for -lrt

Needed when pgqd is built against libevent (--with-libevent)
create-node: validate, accept public location from config
setup_skytools: install grant files under /usr/share/skytools
more newgrants fixes.

mostly works now.

only problem is that londiste_writer needs to be
superuser because of session_replication_role.
That can be fixed with secdef function, but that
means code needs to be installed separately.
cascadeadmin status: wait for threads

Instead Queue.join(), call Thread.join() for each
thread.  Otherwise the thread can be active during
process shutdown and throw weird errors.

After that, calling Queue.join() seems useless; it can
even allow additional failure situations.

Also clarify thread count logic.