#17 Add warning if variable names in DOM conflict

[James E. Ervin]

If you import two doms, there is no check currently to
see if the var names collide.

There should be a warning given to the user if it occurs.

There should be a facility to allow the user to
override the binding variable names for a specific
script's context.

To override the binding var name, a mapping will have
to be maintained per script context ( RunScript class )
to conduct the translation.

To persist the changed var name, a metadata tag of some
sort will have to be added, perhaps a change to the
DOM: tag. Maybe like the following:

* DOM: <URL Plugin String> { oldVarName => newVarName,
... }