PE-1603 - Added 'timestamp' session variable. Contains the current
system (DVE) time if set to DEFAULT or 0. Affects the value returned by
NOW(). Can be overriden by 'dve_repl_slave_timestamp' if set to a
non-zero value.
PE-1603 - Added isNumeric() method to ValueMetadata. TRUE for numeric
variables which values must not be quoted in SET stmts.