Merge "old" SQL variable to "old_mode" sql variable

SQL variable "old" controls boolean server variable old_mode which used in several places.

SQL variable "old_mode" controls set server variable old_behavior.

Make so that SQL "old" variable will set one or several bits in "old_mode" (old_behavior) for compatibility.

Check knowledge base for correspondence description to server behavior (now there told that old_mode replace old but it does not looks like correct)