Implement AsGML(TopoGeometry)

[strk]

The function should produce <gml:TopoPoint>, <gml:TopoCurve> and <gml:TopoSurface> for a given TopoGeometry.

There should be a way for the function to decide about whether to write primitive elements "inline" or to reference them trough xlinks. Such a decision could be driven by an optional second argument being the name of a "visited" table to use for bookkeeping.

A companion for this function would be a triplet of AsGML(<primitive_topology_record>) functions to write the actual <gml:Node>, <gml:Edge> and <gml:Face> tags, each of which should likely also make use of a passed-or-created "visited" table (gml:Face references gml:Edge, gml:Edge references gml:Node)

[strk]

First part is implemented. Doesn't do xlinks/visited table. Accepts a custom prefix. Always outputs GML3 for geometric properties and long srsNames.

TODO: figure an interface for book keeping. This could be the name of a (possibly temporary?) table to query for and register visited primitives.

[strk]

The function now also accept precision and options args (passed to the underlaying ST_AsGML function). Still xlinks/visited to go

[strk]

As of r6732 visited bookkeeping is also ready, as well as tests. Last scan of the dox before closing this.

[strk]

All done as of r6733 . Have fun with topological GML !