Fix CLI popen handling

[fumi]

From the issue of RDF.rb http://github.com/bendiken/rdf/issues#issue/33 and the sample code http://gist.github.com/459459 , it appears that the CLI implementation has a bug where pipes to the sub-process is not closed. It seems that it causes to make zombie processes. The FFI implementation does not have this issue.

[jfieber]

Commit http://github.com/bendiken/rdf-raptor/commit/f9442523ab was supposed to address the zombie-factory behavior, but apparently isn't quite right.