harden dynamic linker library path search

harden dynamic linker library path search

transient errors during the path search should not allow the search to
continue and possibly open the wrong file. this patch eliminates most
conditions where that could happen, but there is still a possibility
that $ORIGIN-based rpath processing will have an allocation failure,
causing the search to skip such a path. fixing this is left as a
separate task.

a small bug where overly-long path components caused an infinite loop
rather than being skipped/ignored is also fixed.