Always call connection_ap_attach_pending() once a second.
Fixes bug 19969; bugfix on b1d56fc58. We can fix this some more in
later Tors, but for now, this is probably the simplest fix possible.
This is a belt-and-suspenders fix, where the earlier fix ("Ask
event_base_loop to finish when we add a pending stream") aims to respond
to new streams as soon as they arrive, and this one aims to make sure
that we definitely respond to all of the streams.