RFC: add a testsuite for libstdc++ pretty-printers

[Benjamin Kosnik]

> I'm not competent to review the code, but I'm very pleased to see a
> way to test the printers.  I've been concerned about them bitrotting
> if we change library internals and forget to change the printers.

Yes! Love these tests, will keep everybody honest. This is also great
example code.

> This should also help us notice if we rely on features of a particular
> version of python or gdb which fail with earlier versions, e.g. python
> 2.6 conditional expressions and gdb 7.1 lazy strings.

Yep. Testresults should be very interesting to watch.

Go for it Tom.

-benjamin