fixes for quota support on NetBSD

Hi!

dovecot-2.2.13 already has quota support for NetBSD, but it's buggy. The attached patches by Manuel Bouyer bouyer@NetBSD.org fix the issues.

There is one thing that's not nice in them: one include is now for "/usr/include/quota.h" since dovecot comes with its own file "quota.h" which is earlier in the search path. Perhaps dovecot's copy can be renamed to dovecot-quota.h or to some other non-conflicting name?

Cheers, Thomas