http: Add http_build_query wrapper

This is necessary so we can sanitize/encode inputs.

include/class.http.php

@@ -111,5 +111,10 @@ class Http {
             exit;
         }
     }
+
+    static function build_query($vars, $encode=true, $separator='&') {
+        return http_build_query(
+                ($encode ? Format::htmlchars($vars) : $vars), '', $separator);
+    }
 }
 ?>