+ make tracing configurable via system properties
  -Decj.typeinference.debug=true/false
  -Decj.typeinference.debug.fine=true/false
  -Decj.typeinference.debug.longNames=true/false
     new: by default show short type names, back to long via this option
+ fix NPE in tracing in BoundSet.incorporate()
+ log failed reduction during incorporation
+ don't log "Added bound" when about to skip
+ better formatting when reduction produces several new constraints
+ print invocation as part of InferenceContext18.toString()
+ show "Infer invocation type ..." before starting that inference