Tests for thread-last.

Updated thread-last tests to conform to the four following criteria as per
this blog post: http://www.reflectionlibrary.co/blog/?p=157
	* Depth of nesting greater than a given level
	* Nesting depth for non-last args less than a given level
	* The call is a top-level threadable call
	* The call is to a function for which treading makes sense
Edited thread-last to conform to new rules.

It passes all the tests, so it must be good, right?

Right?