Documentation.

git-svn-id: http://h2database.googlecode.com/svn/trunk@5815 e6896862-9d19-0410-bfb3-e9fa5d50e656
Synchronize write access (needed for background compact operations)

git-svn-id: http://h2database.googlecode.com/svn/trunk@5816 e6896862-9d19-0410-bfb3-e9fa5d50e656