1: the fi_readers and fi_writers fields of the fifoinfo structure were not
being initialized to 0. This caused the driver to not sleep the first
process to open the fifo--it thought there was already another process to
talk to (most of the time.)
2: fifo_open() was calling tsleep() without unlocking the inode of the fifo
file. This caused *any* subsequent access to the file (even an ls (!)) to
hang forever. Note that this bug was usually masked by bug #1 above.
