#638, checking/configuring in cmake pthread_yield and sched_yield; READLINE_ROOT for better readline control;

Rewritten

Write a function which can be used to check whether a user
exists or not.

Fixes gh-632.

added comments to rtree, added more misc tests for rtree, moved key validation from index to key_def, added NUMBER key type

Weed out 'box' data type for now. A special name can backfire
in the future, when we exteend HASH/TREE/other types.

Add checks for uniqueness.

Disable check of key parts, it was not used any way,
since an explicit check is made in initIterator() and findByKey().

Mark sophia engine as  not supporting RTREE.

Use cached user credentials for global access checks and store
them in a separate fiber key.

This fixes gh-617 and speeds up privilege checks.

@todo: we need to add a linked list of all user sessions
to the user cache, as well as all user setuid functions.
These lists could be used to update privilege cache,
get/update per-user statistics, disconnect sessions
of a dropped user.

Encapsulate error handling in user cache search functions.

Make sure the tests pass under low memory and no memory overcommit.

closes #gh-554

1) server.get_log(); server.seek_once(msg) -- since we get log object
2) server.logfile_pos.seek_once(msg) -- since the start of server

This patch also fixes incorrect offset calculation in buffer
with multiple responses:

    self.rbuf = string.sub(self.rbuf, off + 1)

`_func' space recovered before `_user' and auth_token can't
be retrived during creating struct func_def.