Adjustments to _copy_internals()

Adjustments to _copy_internals()

We are looking to build a generalization of copy_internals(),
so move out any special logic from these methods.   Re-implement
and clarify rationale for the Alias doesnt copy a TableClause rule as
part of the adaption
traversal, establish that we forgot to build out comparison and cache
key for CTE, remove incomplete _copy_internals() from GenerativeSelect
(it doesn't handle the order_by_clause or group_by_clause, so is incomplete)

Change-Id: I95039f042503171aade4ba0fabc9b1598e3c49cf