Speedup initial meta store update by only fetching public tables

	* glom/libglom/connectionpool_backends/backend.h:
	* glom/libglom/connectionpool_backends/postgres.h:
	* glom/libglom/connectionpool_backends/sqlite.h: Added
	get_public_schema_name() virtual function and implementations for both
	backends.

	* glom/libglom/connectionpool.cc: Only update the meta store tables
	for the public schema of the corresponding backend. This considerably
	speeds up the initial meta store update. This requires latest libgdamm
	from git.