Better fix for the problem addressed by rev.1.79: don't loop in fifo_open() waiting for another reader or writer if one arrived and departed while we were waiting (or a little earlier).
Better fix for the problem addressed by rev.1.79: don't loop in
fifo_open() waiting for another reader or writer if one arrived and
departed while we were waiting (or a little earlier).

Rev.1.79 broke blocking opens of fifos by making them time out after 1
second.  This was bad for at least apsfilter.

Tested by:	"Simon 'corecode' Schubert" <corecode@corecode.ath.cx>,
		Alexander Leidinger <Alexander@leidinger.net>,
		phk
MFC after:	4 weeks

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase