Improved code for linking pathnames

Now raises a warning if more than one path found for a search, an
exception if no paths are found.  Briefly added ability to automatically
wild-card the D-part for slices, but ran into data organization problem.
Direct linking to extract files.

Added the ability to specify extract files for each alternative for
testing.  Not a recommended technique, but over-rides file search code
for files where the alternative doesn't match the F-part.