Allow $new->chmod($old) to copy mode of another path

[grr]

I propose allowing chmod to accept a path as an argument, from which it can copy the mode to apply to the the original path. Currently the user has to do:

$new->chmod($old->stat->mode & 07777);

It would be a lot more convenient to do:

$new->chmod($old)

This is similar sugar as request #311 .

[ap]

Same API design objection as over there ($new->chmod($old) is not very skim-friendly) and same suggestion as to how to resolve it.