Delay reusing ids to make protocol more robust

Delay reusing ids to make protocol more robust

Ronnie and I tracked down a bug which seems to be caused by a node
running so slowly that we timed out the request and reused the request
id before it responded.

The result was that we unlocked the wrong record, leading to the
following:

	ctdbd: tdb_unlock: count is 0
	ctdbd: tdb_chainunlock failed
	smbd[1630912]: [2010/06/08 15:32:28.251716,  0] lib/util_sock.c:1491(get_peer_addr_internal)
	ctdbd: Could not find idr:43
	ctdbd: server/ctdb_call.c:492 reqid 43 not found

This exact problem is now detected, but in general we want to delay
id reuse as long as possible to make our system more robust.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>