Make default url resolver a separate function.

jsonld.php

@@ -171,6 +171,18 @@ function jsonld_resolve_url($url) {
     return call_user_func($jsonld_default_url_resolver, $url);
   }
 
+  // default JSON-LD GET implementation
+  return jsonld_default_resolve_url($url);
+}
+
+/**
+ * The default implementation to retrieve JSON-LD at the given URL.
+ *
+ * @param string $url the URL to to resolve.
+ *
+ * @return the JSON-LD.
+ */
+function jsonld_default_resolve_url($url) {
   // default JSON-LD GET implementation
   $opts = array('http' =>
       array(