Namespaces are often used just for forward declarations of third
party classes, e.g. boost or even std.  We don't want to wrap these,
we only want to wrap namespaces that are part of our API.  For now,
that means wrapping namespaces that define useful constants.

Change-Id: Icdd111c2e8b3c9031cde1a5409a74f3d09767e69