A new FTBFS every day

[Daniel van Vugt]

Martin,

Since we moved CI to saucy only, we keep landing code that fails to 
build on gcc-4.7 (raring) for various reasons.

I know we don't care about raring as much as saucy, but we do care about 
Mir being consumable in other distros. And that means broad-ish support 
for gcc versions.

Can we add raring CI support back in so these build problems get caught 
in time?

- Daniel