Please add optimization support for foreign keys in materialized tables

The issues came up in the following discussion

https://developer.jboss.org/message/989502#989502

> 1a) Are the constraints (indexes, foreign keys) now used to optimize queries in materialized tables or not?
 
Pk, Unique Key, and Indexes on the view will result in the creation of an index on the materialization target table and are fully utilized in planning decisions.  Things are a little more complicated with foreign keys.  Currently they are not propagated onto the generated materialization target table metadata, so they are only considered in pre-planner activities, such as rewrite, before the view reference is replaced with the materialization target - but there aren't meaningful optimizations being made at that time based upon foreign key.  There are couple of narrow situations where that information would be useful, so it probably should be added.