MVStore: descending indexes with "nulls first" did not work as expected (null was ordered last). 

git-svn-id: http://h2database.googlecode.com/svn/trunk@5703 e6896862-9d19-0410-bfb3-e9fa5d50e656
Bugfix

git-svn-id: http://h2database.googlecode.com/svn/trunk@5704 e6896862-9d19-0410-bfb3-e9fa5d50e656