Adding deep freeze functionality to nodes to make outputs immutable

Hello sho, 

Please review the following commits I made in branch 'jeremy-utils'.

38f344463c5efe9410349e7ed8e5b397f550177e (2013-02-26 15:56:54 -0800)
Private nodes aren't frozen

f13bc44c86cdad378a872ac42eb4e2fa9c7ac098 (2013-02-26 15:49:40 -0800)
Adding deepFreeze() support

R=sho