[Talk-GB] C roads again

[Will Phillips]

This is a widespread problem and I wouldn't oppose a mechanical edit in 
this case. The one concern I have is the rare cases where C road 
references really do appear on signs, but perhaps even then official_ref 
is appropriate.

Similarly, some rights of way references appear on signs: I recall this 
is common on the Isle of Wight. Should this influence whether ref or 
prow_ref is used?

Cheers,
Will