rework gathering of serialization information. (#479)

rework gathering of serialization information. (#479)

The existing method broke encapsulation to generate the combined
list of regular and style based formats.  It required access to
xcsv_vecs, which is only present in LegacyFormats.  Until recently
it also required access to xcsv_file.

The existing method also leaked memory, although the use case was
such that the program always exited shortly thereafter.

All these issues are resolved during unification by gathering all the
necessary information and passing that on to serialization.  This
information is gathered from different places for regular and style
based formats.