Unify event logging and debug tracing.
- tracing facilities are now enabled with -DTRACING, and -DDEBUG additionally enables debug-tracing. -DEVENTLOG has been removed. - -debug now implies -eventlog - events can be printed to stderr instead of being sent to the binary .eventlog file by adding +RTS -v (which is implied by the +RTS -Dx options). - -Dx debug messages can be sent to the binary .eventlog file by adding +RTS -l. This should help debugging by reducing the impact of debug tracing on execution time. - Various debug messages that duplicated the information in events have been removed.