CTFE unit tests

[Jacob Carlborg]

Recently I added a new trait to get all the unit tests functions from a 
module. With this in place, among other things, it's possible to do unit 
tests for CTFE functions. Here's a quick try:

http://pastebin.com/Kk0in3bD

What's missing is CTFE-able "writeln".

It's also possible to implement named unit tests in library code, now 
when it's possible to access UDA's from the unit test functions.

-- 
/Jacob Carlborg