_locate_source in post-script.sh does not recurse

[camscale]

I'm pretty sure _locate_source in core/post-script.sh is meant to recurse at https://github.com/camh-/lbr/blob/master/core/post-script.sh#L237 - I probably renamed _locate to _locate_source and did not update this reference.

Double check this and fix it if needed.

Perhaps I should write some unit tests too.