Transport all flags into expand loop.
Push full flags list to all repack routines. Makes it easier to extend
functionality then.
API EXTENSION: introduce new flag FLAG_NOSORT to avoid sorting the output
data structures according to their content. This leaves the original readout
order untouched. Use with care.

This fixes psi46/pxar#109 without actually breaking the API and introducing
global variables which might (or not) be initialized and filled.