Make java2mat an internal function only?

[Rik]

All,

I notice that java2mat has no documentation, just "Undocumented internal
function".

Using grep, I can't see that it is used anywhere in the core either. 
Should we rename this to "__java2mat__" to indicate that it really is an
internal function?  Eventually we could even deprecate it if no one is
using it, but I would start with renaming it.

--Rik