MetaTableAccessor.getMergeRegions() returns parent regions in random order

The multi-region merge patch has changed the behaviour of the MetaTableAccessor.getMergeRegions() method. Earlier, the parent regions were returned in the same order that they were passed to mergeRegion().

The patch has changed this to return the regions in random order. To be more precise, the parent regions are stored in random order in Meta.

I propose storing and returning the parent regions in ascending order.