Class GetQuota.

Inherits Command. Inherited by GetQuotaRoot.

The GetQuota command implements the GETQUOTA command defined by RFC 2087. It is the only part Archiveopteryx really implements; we want to report usage, not impose quotas.

Usage is defined as the sum of RFC822-format size, in kb. This is usually much bigger than the actual number of kilobytes used by the database for storing the mail (at one site by a factor of four), but it'll do for reporting usage.