test_fake_connection: Avoid unnecessary warnings about metadata.

	* glom/libglom/connectionpool.cc: Avoid printing exceptions to stderr
	about failed attempts to get types and tables metadata, because
	this is not used by fake connections, for instance by java-libglom.
	There will be a warning later if it is really used.
	* glom/libglom/db_utils.cc: Add some comments.