Test revoke a privilege from a role using a different grant path.

Implement granted privilege cache in struct user.

Reload user privileges from system spaces and
rebuild the cache whenever a grant or revoke occurs..

Implement revoking privileges from a role.
Basic tests pass.

Do not rebuild the privilege cache of objects
for which it can't have changed with a grant
or revoke.

Optimize rebuild_effective_grants().

Make role.test idempotent.

Make grant and revoke robust to malformed arguments.
Fix bugs in schema.lua, related to incorrect arguments
for grant/revoke.

Added method remote:reload_schema()

Introduce 'public' role.
Auto-grant 'public' to every user.
Update the snapshot.

Track granted roles.
Represent roles granted to a user with a bitmap.
Disallow loops in role grants.
Add tests for box.schema.user.grant('username', 'rolename')
Add basic tests for loops in grant sequences.

Rewrite largely buggy code in authentication token lookup.
Do not waste space on authentication token bitmap, correctly
check for overflow of the bitmap.

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.

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.

Extract the non-failing parts of the original patch by Roman.
Make an attempt at finding why coeio_custom is crashing when
replication_source is changed quickly - no success yet.