rdup-up: handle reversed (-R) rdup dumps

[koukou73gr]

There is an inherent problem with normal dumps: directory a/mtimes don't get reset to the stored value. Reverse dumps suffer no such problem, but rdup-up does not support them as it is.

This is my attempt to support reverse dump in rdup-up, following the logic used when EACCESS is returned. So, in response to an ENOENT error when creating an object, attempt to make the parent path and then try the operation. If this fails log it and move on.

****This relies on dir_parent() not returning the trailing /