Qmail-SQL - Maildir++ support

This patch adds maildirquota (Maildir++) support to qmail-pop3d, qmail-local and sqlcreatehomedir. It was created because when using some other Maildir++ enabled programs (Maildrop, Courier-IMAP, ...) which access the same Maildir, then quota information is not modified by qmail-pop3d after deleting message and by qmail-local after local delivery.

This patch is tailored to fit to Qmail-SQL (SQL enabled Qmail), but it may be used on original qmail with few modifications.

Note: Qmail-SQL uses it's own quota mechanism in qmail-local by calling `du' (disk usage) on user's Maildir every time, which is not very effective. This mechanism works with sizes in KILOBYTES, but Maildir++ quota mechanism works with BYTES, so you have to update quota column in your qmail table/database.

This patch was inspired by the Maildir++ patch by Bill Shupp, but his patch used old maildirquota functions. This patch uses same maildirquota functions as Courier-IMAP 2.2.1 does.

See the Maildir++ specification by Sam Varshavchik on www.courier-mta.org.