make unpack use spacem logic, to reduce code repetition

[Fred T. Hamster]

can we refine spacem, renlower, etc to support telling us the new name it _would_ use rather than always doing the rename?

maybe just a cmd line arg that says "only report, don't rename".
just a new flag and this is done?
and what it supports is nice: we can use that "show us a better name"
logic in any script that wants to make a clone of a directory and use
a similar name to the original.

this would get us out of some pitfalls of trying to create new names based on hosed original files.