Sign CLA.

Signed-off-by: Piotr Sikora <piotr.sikora@frickle.com>

CONTRIBUTORS.txt

@@ -74,3 +74,4 @@ Simon Josi, 2012/06/08
 Sam Cooke, 2012/06/08
 Frederic Junod, 2012/06/08
 Roberto Gaiser, 2012/06/08
+Piotr Sikora, 2012/06/08