#5 object from different modules may reference each other

[Driss Ghaddab]

An object from module A should be able from its own
thread A to reference and use an object from module B.
The needed operations are: set/get properties, execute
method.

Reference counting may be needed to avoir race
conditions where an object from module B used from
thread A is being deleted by B.

Branch cmo--threadsafe-objects has been created to
implement this feature.