fix deadlock in concurrent LOB update

git-svn-id: http://h2database.googlecode.com/svn/trunk@4826 e6896862-9d19-0410-bfb3-e9fa5d50e656
the field "small" can be declared final

git-svn-id: http://h2database.googlecode.com/svn/trunk@4827 e6896862-9d19-0410-bfb3-e9fa5d50e656
"handler" field can be declared final

git-svn-id: http://h2database.googlecode.com/svn/trunk@4828 e6896862-9d19-0410-bfb3-e9fa5d50e656