EIGENBASE: rel: make HomogeneousUnionToIteratorRule easy to subclass.
EIGENBASE: rel: make HomogeneousUnionToIteratorRule easy to subclass.

[git-p4: depot-paths = "//open/dt/dev/": change = 4098]

LucidDB/luciddb,LucidDB/luciddb,LucidDB/luciddb,LucidDB/luciddb,LucidDB/luciddb,LucidDB/luciddb,LucidDB/luciddb,LucidDB/luciddb,LucidDB/luciddb