Update Hystrix for breaking changes in RxJava 0.12

Basically throwing random "? super T"s all over the place and switching
from Func1 to OnSubscribeFunc. Tests pass. Please review for dumb
mistakes.
RxJava [0.11,0.12)

Trying to fix https://github.com/Netflix/Hystrix/issues/178

I tried this on local build, it worked. Trying now on build system.
[Gradle Release Plugin] - pre tag commit:  '1.3.4'.
[Gradle Release Plugin] - new version commit:  '1.3.5-SNAPSHOT'.
rxjava-core:[0.13,0.14)
Upgrade to Rxjava 0.13

Merge branch 'rxjava-0.12' of https://github.com/daveray/Hystrix into rxjava-0.13

Conflicts:
	hystrix-core/build.gradle
Merge pull request #179 from benjchristensen/rxjava-0.13

RxJava 0.13