BuxtonArray/list_keys/checks

So all comments were answered and corrected, make check brought up to date and working with new BuxtonArray based message serialisation API (Which, btw, is so much cleaner to work with :)) and a new check added specifically for BuxtonArray.

That about wraps up list_keys :) 

P.S. We can look later at whether to bother adding SMACK checks in list_keys, because it doesn't actually disclose any information. I'd like to leave those until *after* Mike gets his configurator in, so that my local build works properly (autotools is having heart-attacks outside of make check)