MVStore: support two compression levels; measure read and written bytes; ascending iteration over entry set

git-svn-id: http://h2database.googlecode.com/svn/trunk@5530 e6896862-9d19-0410-bfb3-e9fa5d50e656
An archive tool that uses compression and de-duplication (is faster and compresses better than 7zip / pkzip for large directories if there are many duplicates)

git-svn-id: http://h2database.googlecode.com/svn/trunk@5531 e6896862-9d19-0410-bfb3-e9fa5d50e656