keyfunc.sh.in: Don't let `userv' gobble our input.

keyfunc.sh.in: Don't let `userv' gobble our input.

Unfortunately, `userv' has a bad habit of eating our stdin, whether it
needs it or not.  (This is a result of the `cat' processes and pipes
strung between the calling and service environments.)  To prevent this
from gobbling our input, which we might actually want to process
ourselves in some way, make sure that we let it chew on something less
important.  Like `/dev/null', say.