CONTRIB: initiate a debugging suite to make debugging easier

CONTRIB: initiate a debugging suite to make debugging easier

The goal is to have a collection of quick-n-dirty utilities that make
debugging easier and that can easily be modified when needed. The first
utility in this series is called "flags". For a given numeric argument,
it reports the various known combinations of flags for channels, streams
and so on. This way it's easy to copy-paste values from the CLI or from
gdb and immediately know what state a stream-interface or connection is
in.