During the `Head` election phase, we now introduce the following
additional criterion:
When processing a `GenericRegion` nested into an outer one (its
`ParentRegion`), if the inner `Region` contains the block that has been
elected as `Head` of the `ParentRegion`, we also force that block to be
the `Head` of the inner `GenericRegion`.
We add a unit test to check this behavior.
Andrea Gussoni
2ba365bc45