SPARQLStore / Fix redirect target resource

Doing substr( $rediTargetUri, 0, strlen( $wikiNamespace ) ) will return
`http://example.org/id/http://example.org/id/` which is not what we want
and instead we expect something like `http://example.org/id/Property-3AFoo`
Merge pull request #472 from SemanticMediaWiki/sparql-redirect

SPARQLStore / Fix redirect target resource