Added myself to Contributors (pull request 1069)

CONTRIBUTORS.txt

@@ -121,3 +121,4 @@ Thomas Meson, 2012/08/28
 Daniel Lundin, 2012/08/30
 Alexey Zatelepin, 2012/09/18
 Sundar Raman, 2012/09/24
+Henri Colas, 2012/11/16