The call:

int fb_shutdown (int type, int milliseconds);

where "type" is one of:

* fb_shutdown_count -- just return number of active connections
* fb_shutdown_attachments -- block new attachments, wait (see below)
for pending to exit
* fb_shutdown_transactions -- block new attachments and transaction,
wait for pending to finish
* fb_shutdown_verbs -- block new calls, wait for pending to finish
* fb_shutdown_immediate -- stop pending verbs w/ clean error
* fb_shutdown_panic -- shutdown as fast as cleanly possible

and "milliseconds" is a period to wait, where milliseconds < 0 means
don't wait, milliseconds == 0 means wait indefinitely, and milliseconds

> 0 means wait for that number of milliseconds before timing out.

All flavors return the number of active connections.