[Dovecot] improve error messages with quotes

[Timo Sirainen]

On 19.7.2012, at 19.02, Radim Kolar wrote:

> I propose to improve error messages but inserting quotes. I spent good time until I looked into source code to find right meaning of error message.
> 
> I would like them in following format:
> 
> namespace configuration error no 'hidden=no' namespaces

I think this is clearer: http://hg.dovecot.org/dovecot-2.1/rev/0abb9b0a54db