status: add the --change option to display files changed in a revision
This option is similar to the one already used for the diff command.
Unfortunately, the c and C short option are already used for status, so there
is no corresponding short option. However, there is no short option for --rev
either, so that's consistent.
# should print nothing
# should fail
abort: path 'b/x' is inside repo 'b'
abort: path 'b/x' is inside repo 'b'
# should fail
abort: path 'b/x' is inside repo 'b'
# should arguably print nothing
# should fail
abort: path 'b/a' is inside repo 'b'