[MIN] XQuery: moving check for duplicate namespace declarations
[MIN] XQuery: materialize results swalloed by prof:void()
[FIX] DBLocking: NPE fix
[MOD] Core, locking: downgrade function added to Locking interface
[MIN] comment
[MIN] XQuery, prof:void() signature fixed
[ADD] Core, Locking: downgrading (locks.downgrade() not acticated yet)