Add a BT_CURSOR_EXACT operation to btree_cursor_get. It behaves like
BT_CURSOR, but fails if the key is not found.

Set errno to appropriate values when returning failure in btree. Make btree
functions only return success or failure (-1 or NULL). Update callers to
check errno.

Don't expose typedefs of pgno_t and indx_t in the public header file, move
them to btree.c. Also don't use exact-width integer types in public btree api.

Fix value clash in btree flags BT_FIXPADDING and BT_NOSYNC.

Append a "tombstone" meta page after a database has been compacted. This
allows other processes to pick up the change and re-open the file.

Initial import of ldapd, a small LDAP daemon. Work in progress.

ok deraadt@ jacekm@ gilles@ back@ henning@ blambert@