lib-storage: Removed mailbox list backend-specific mailbox name/pattern validation. The virtual name validity is independent of the backend. The physical name is always used for paths in filesystem, so it can also be verified with common code. Backend's mailbox_dir and storage's internal directories can also be checked. There's nothing else left really.

lib-storage: Finished previous get_mailbox_flags() change.

lib-storage: Changed mailbox_list.iter_is_mailbox() API. --HG-- branch : HEAD

lib-storage: Mailbox deletion API changed. Mailbox deletion should now be free of race conditions. The actual file deletion code is now responsibility of mailbox_list backend. --HG-- branch : HEAD

Avoid using PATH_MAX. --HG-- branch : HEAD

Changed .h ifdef/defines to use <NAME>_H format. --HG-- branch : HEAD

Added support for multiple mailbox list patterns. --HG-- branch : HEAD

s/mask/pattern/ for mailbox listing. --HG-- branch : HEAD

mailbox_list_iter_next() returns now const pointer. --HG-- branch : HEAD

Mailbox list indexing and related changes. Currently works only with maildir and mmap_disable=no. This allows doing STATUS to synced mailboxes without opening their index files at all. --HG-- branch : HEAD

Initial code for separation of mailbox accessing and directory layout handling. It's not yet possible to change the default layouts though. --HG-- branch : HEAD