Reimplemented Last operation
Convert 'last' from non-blocking to blocking to match Rx.Net

See https://github.com/Netflix/RxJava/issues/57#issuecomment-14253118 for background.

NOTE: This is a breaking change thus we are bumping the version from 0.5.x to 0.6.x

Manual merge of branch 'last' of git://github.com/mairbek/RxJava into issue-57-last

Conflicts:
	rxjava-core/src/main/java/rx/Observable.java
Merge pull request #184 from benjchristensen/issue-57-last

Convert 'last' from non-blocking to blocking to match Rx.Net