Adds files to control list set up in the virtuoso.ini file.
The return value is not specified and may be changed in future versions.
ld_dir ('/data8/2848260', '%.gz', 'http://bsbm.org');
would load the RDF in all files ending in .gz from the directory given as first parameter. The RDF would be loaded in the http://bsbm.org graph.
If NULL is given for the graph, each file may go to a different graph specified in a separate file with the name of the RDF source file plus the extension .graph.
A .graph file contains the target graph URI without any other content or whitespace.