lei: support "-C" to chdir in all sub commands

lei: support "-C" to chdir in all sub commands

We'll also support "-C" at the end of most commands to give
users a little more flexibility when building command-lines.
This conflicts with "lei daemon-kill -CHLD", so that's
special-cased since "-C" makes no sense with daemon-kill,
anyways.

Unlike "git show", the to-be-implemented "lei show" will diverge
and enable "--find-copies[=<n>]" by default, so "-C[<n>]" won't
be necessary.