With PostgreSQL 8.3, there's a new concept called "operator families".
An operator class is now part of an operator family, which can contain
cross-datatype operators that are "compatible" with each other.

ORCA doesn't know anything about that. This commit updates the
Translator files to refer to OpFamily instead of 'OpClasses'.

ORCA still doesn't take advantage of this, but at least we are using
operator families in operator classes' stead to make indexes work.
Signed-off-by: NHaisheng Yuan <hyuan@pivotal.io>