Road to 2.5 improvements and fixes

- Now namespaces and classes are stored in an internal hash so this
increases performances as no more searchs are required when importing
namespaces. Big advantage!

- Now source code will prevent that jOOPL would be loaded more than once
in the same page.

- Now $namespace.register supports storing the registered/imported
namespace as scope function argument in addition to doing so also on
"this" keyword.