Fixes #3078 .  I have extended SideSetsAroundSubdomain to include optional specification of a normal direction.  This involved a lot more screwing around than i anticipated.  Amend: got rid of a tab.  Amend: corrected supid programming involving Point.  Amend: normal -> _normal in constructor.
Merge pull request #3079 from WilkAndy/feature_3078

Fixes #3078 .  I have extended SideSetsAroundSubdomain to include option...