several optimizations

  - when looking for all resource instances, first list all ports and then
    select only those for which options file(s) exist(s) - this is opose to
    what we had previously (scanning options files first); this eliminates
    the need for double scanning of options files, cumbersome port searches
    and querying for make variables,
  - querying for make variables (such as OPTIONS_FILE) is no longer
    performed; this information is now obtained by other means
release 0.2.1