BabuDB: added lock for BabuDB meta operations like creating/deleting/copying...

BabuDB: added lock for BabuDB meta operations like creating/deleting/copying databases. Removed former lock owned by the Checkpointer

git-svn-id: https://babudb.googlecode.com/svn/trunk@133 d4c7dd96-b7b2-11dd-893d-d98698f66bbf