Basic takeUntil implementation
Tests for TakeUntil
Merge branch 'master' into TakeUntiFunctional

Conflicts:
	rxjava-core/src/main/java/rx/Observable.java
Refactored TakeUntil operator
Updated logic to match Rx.NET
Refactored TakeUntil to use TakeWhile.
Cleaned up comment
Merge pull request #151 from mairbek/TakeUntiFunctional

Implemented TakeUntil operation