Merge branch 'first-firstDefault' of git://github.com/jmhofer/RxJava into operator-first-merge

Conflicts:
	rxjava-core/src/test/java/rx/ObservableTests.java

This merges pull request ReactiveX/RxJava#357

Also aliased first with takeFirst to match takeLast.

Author: benjchristensen