Debug tool-provided event handlers

One of the most important things a debug tool must do to be called by Language Environment is provide two logical event handlers:

• An event handler to handle general Language Environment events. When the debugger initializes, it must place the address of this event handler in the member list slot that corresponds to the debugger's member identifier. If the debugger has no member identifier, it should not modify any slots in the member list. If that slot is already initialized, then two members are using the same member identifier, and debugger initialization should fail.
• An event handler to handle debug events. The address of this event handler is maintained by Language Environment in the PCB field, CEEPCBDBGEH. When Language Environment initializes, this field is initialized to zero; when Language Environment loads the debug event handler, it sets this field to the address of the debug event handler.