1. dbug state is now local to a thread
2. new macros: DBUG_EXPLAIN, DBUG_EXPLAIN_INITIAL,
   DBUG_SET, DBUG_SET_INITIAL, DBUG_EVALUATE, DBUG_EVALUATE_IF
3. macros are do{}while(0) wrapped
4. incremental modifications to the dbug state (e.g. "+d,info:-t")
5. dbug code cleanup, style fixes
6. _db_on_ and DEBUGGER_ON/OFF removed
7. rest of MySQL code fixed because of 3 (missing ;) and 6
8. dbug manual updated
9. server variable @@debug (global and local) to control dbug from SQL!
a. -#T to print timestamps in the log