Scala Adaptor Improvements by Erik

There are many important improvements by Erik on the branch https://github.com/Applied-Duality/RxJava/tree/RxJavaBugFixes , and I'd like to have them on Netflix:master, so that everyone works on the same code, and that we can avoid duplicate work, since some changes I'd like to do require changes that Erik has already made. @headinthebox hope you're ok with this.