hitting DML which is causing us to open up the
ColumnCollection structure a bit, as we do put anonymous
column expressions with None here. However, we still want
Table /TableClause to have named column collections that
don't return None, so parametrize the "key" in this
collection also.
* rename some "immutable" elements to "readonly". we change
the contents of immutablecolumncollection underneath, so it's
not "immutable"
Change-Id: I2593995a4e5c6eae874bed5bf76117198be8ae97
Mike Bayer
4e754a8914