8162546: change hidden options -Xdebug to --debug, -XshouldStop to --should-stop, and -diags to --diags
Reviewed-by: mcimadamore

8161020: javac, fold stop compilation options
Reviewed-by: mcimadamore

6970584: Flow.java should be more error-friendly
Summary: Added a post-attribution visitor that fixup uninitialized types/symbol in AST after erroneous attribution
Reviewed-by: jjg