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.

Do not return extra result from tuple:__index method.

packages.

Marshall replication using the primary port.

Split iproto requests into two categories: DML and admin.  Change
PING request code to 64, to lay within admin request range.
Perform administrative requests synchronously, without pushing
them into an event queue.
Add a new administrative request, IPROTO_SUBSCRIBE.

Use dynamic memory for struct iproto_request. Introduce memory
management.

Remove replication_port from the configuration file and
update tests.

Fix the test runner so that it correctly generates
replication_source to point to the primary port.
Add variable arguments to IllegalParams.
Move replia-related recovery methods to a new header, replica.h.

Remove a debug printout from box.net.lua

Update tests.

Conflicts:
	.gitignore
	cmake/BuildMisc.cmake
	cmake/compiler.cmake
	include/avl_tree.h
	src/box/avl_tree_index.h
	test/unit/avl_tree.c
	third_party/qsort_arg_mt.c

'print_log'`

Conflicts:
	src/box/lua/box_net.lua
	test/box/ipc.test
	test/box/net.box.result