improve CREATE LINKED TABLE docs

git-svn-id: http://h2database.googlecode.com/svn/trunk@5006 e6896862-9d19-0410-bfb3-e9fa5d50e656
new test case to verify query cache being dropped when table structure changes

git-svn-id: http://h2database.googlecode.com/svn/trunk@5007 e6896862-9d19-0410-bfb3-e9fa5d50e656