MVStore: use a different free space algorithm (pluggable now)

git-svn-id: http://h2database.googlecode.com/svn/trunk@4982 e6896862-9d19-0410-bfb3-e9fa5d50e656
Prepare release.

git-svn-id: http://h2database.googlecode.com/svn/trunk@4983 e6896862-9d19-0410-bfb3-e9fa5d50e656