This reverts commit c6cf352d.

hmmm, not quite right

and even then, only in specific situations, so simplify accordingly

and removing them exposes a bug in DataType.getTypeFromClass, which we can't fix right now

clean up some javadoc and some throws clauses

Create UndoLog only when necessary and remove outdated code

Remove some PageStore+MVCC leftovers

Fix inconsistencies in checks for transaction isolation level

Fix issues with testing on latest Java versions

# Conflicts:
#	h2/src/main/org/h2/mvstore/tx/TxDecisionMaker.java

Leftovers handling

Fix for issue #1220

merge