With -x, an operand under another operand is kept and walked on its
own when the walk of the deepest kept operand above it cannot reach
it: some directory from it (from its directory, for a regular file) up
to but not including that operand is on a different filesystem than
that operand. Below a kept operand, the rule keeping records under a
directory -x did not enter covers only directories its own walk did
not enter, so records of files gone from it are deleted.
The new tests stub the devices and share their scan steps with the
test for #99. Comments and
README sentences on operands dropped before the walk now also hold
with -x.
Model: opus-5-5
sneak