This module analyzes filename and tries to unpack it.
Module requires for running: archive
Module requires for init: package
Module defines phase: unpack after PREPARE_UNPACK
Module uses phase: unpack
Module uses phase: package
filename: file name to be checked
returns $pwiz_result: file name without extension
returns $unpack_seq: unpacking command
returns $unpack_priority: priority for unpacking (if more formats exist)
Check archive type and prepare unpacking sequence.
Module uses phase: _eval unpack '$unpack_seq "$PWIZ_SOURCESDIR/${package_uri
Module uses phase: unpack unpack_search_dirname
Module uses phase: _eval unpack 'cd "$unpack_dirname"'