refactory.

to support multiple engines.

deprecated connector_c tests

Add new system spaces _user and _priv to store users,
their passwords and their privileges.
Implement an authentication request in iproto protocol

Add a system space _func to store presistent information
about Lua functions. A function is now a subject
to ownership and privilege control.

Use MySQL-style sha1-double-hashing authentication by default.

Implement new Lua functions:

box.session.su()
box.session.uid()
box.schema.user.create()
box.schema.user.drop()
box.schema.user.grant()
box.schema.user.revoke()
box.schema.func.create()
box.schema.func.drop()

Store space creator in space definition.

What this patch doesn't implement:

- privilege checks in replication
- authentication of replication slaves
- exhaustive test coverage

Conflicts:
	src/box/tuple.cc
	src/box/tuple.h
	test/box/lua.result
	test/box/lua.test

This patch converts space:iterator() to be compatible with Lua
for-in loop conventions. The most important change is that
generating function now returns *state* as its first result:

    for _state, val in space.index[0]:pairs() do work(val) end

New syntax follows the best practices of Lua community and makes
index API to be more consistent with pairs() and tuple iterators.

This change partially restores pairs() logic as it was implemented
before 49875615.

This patch introduces backward-incompatible changes to select()
and adds couple new methods:

  * index:select(key) -> tuple, tuple, ... was changed to
    index:select(key, opts = {}) -> { tuple } where opts can be

       - iterator = ALL if key == nil or key == {} | EQ otherwse
       - offset = 0
       - limit = unlimited

  * index:get(key) -> tuple | nil | error on more than one tuple
    a wrapper for select() to get the single tuple

  * space:put(tuple) -> tuple
    an alias for space:replace() (to provide integrity with get())

Test suite, box.space and box.net.box API were also updated to
meet changes.

This patch replaces Lua/C bindings to iterator by FFI.

Minor changes - fix msgpack.decode for zero-size arrays and update
line numbers in result files.