Use containers of labeled search paths instead of individual members

Manage classes of search paths in labeled containers.  This removes the
need to have a seperate member variable for each type of search path, but
also allows path types to be grouped togethor in various different ways
and manipulated as subsets of the full set of search paths.
Merge topic 'refactor-search-path-construction' into next

1abd7cd9 Use containers of labeled search paths instead of individual members