add exclusive/shared mode of attempted lock to deadlock details message for improved debugging

git-svn-id: http://h2database.googlecode.com/svn/trunk@5918 e6896862-9d19-0410-bfb3-e9fa5d50e656
Fix bug which could generate deadlocks when multiple connections accessed the same table.

git-svn-id: http://h2database.googlecode.com/svn/trunk@5919 e6896862-9d19-0410-bfb3-e9fa5d50e656
use a ConcurrentHashMap as a Set to avoid taking the lock where possible

git-svn-id: http://h2database.googlecode.com/svn/trunk@5920 e6896862-9d19-0410-bfb3-e9fa5d50e656
Some places in the code were not respecting the value set in the "SET MAX_MEMORY_ROWS x" command

git-svn-id: http://h2database.googlecode.com/svn/trunk@5921 e6896862-9d19-0410-bfb3-e9fa5d50e656