dl_load(): Require at least one argument
dl_load(): Require at least one argument

The implementatshion fashion of usage checking
 1. enables us to merge it with the 'must augment $PATH' check and
 2. allows us to detect whether $dl_needed became unset (which is con-
    sidered an internal error!).
As an aside, it helps getting rid of empty case labels, which IMHO boosts
aesthetics ;-)

donkarlos/libdl-sh