When the notion of a connection class with a generic set of method was
invented, the very flexible specification formats available for the file
based sources where not integrated into the new connection system.
This patch provides a new connection class md-connection with a specific
sub-protocol (after opening a connection, the caller is supposed to loop
around open-next-stream) so that it's possible to both properly fit into
the connection concept and to better share the code in between our three
implementation (csv, copy, fixed).
That's the big refactoring patch I've been sitting on for too long.
First, refactor connection handling to use a uniformed "connection"
concept (class and generic functions API) everywhere, so that the COPY
derived objects just use that in their :source-db and :target-db slots.
Given that, we don't need no messing around with *pgconn* and *myconn-*
and other special variables at all anywhere in the tree.
Second, clean up some oddities accumulated over time, where some parts
of the code didn't get the memo when new API got into place.
Third, fix any other oddity or missing part found while doing those
first two activities, it was long overdue anyway...
