Moved GUID code to liblib. Use guid_128_t type consistently everywhere.

lib-mail: Make a mail_guid_128_t typedef.

Keep track of expunged messages' GUIDs and expose them via mailbox_get_expunges(). The message GUIDs are stored in expunge records to transaction log. Before doing the final expunge, Maildir and dbox verify that the GUID in expunge request matches the current actual GUID. The GUID is stored in 128 bit field. If the real GUID isn't 128 bit, the bits are taken from SHA1 of the GUID. --HG-- branch : HEAD

Moved keyword_indexes array type to lib-mail. --HG-- branch : HEAD

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

Recent flag handling rewrite. Still not perfect with maildir. --HG-- branch : HEAD

Array API redesigned to work using unions. It now provides type safety without having to enable DEBUG, as long as the compiler supports typeof(). Its API changed a bit. It now allows directly accessing the array contents, although that's not necessarily recommended. Changed existing array usage to be type safe in a bit more places. Removed array_t completely. Also did s/modifyable/modifiable/. --HG-- branch : HEAD

Initial support for keywords. Syncing to mbox/maildir doesn't work yet. --HG-- branch : HEAD

s/custom flags/keywords/ --HG-- branch : HEAD

importing new index code. mbox still broken. --HG-- branch : HEAD