Explicitly close net.box connection on error.

Partially reverts squashed 316d4e3a

iproto thread can add quirks to thread scheduling, replace
single-call yields with yields in a loop.

Conflicts:
	debian/changelog
	debian/control

 tarantool-lts-client (1.5) and tarantool (1.6)
 have file /usr/bin/tarantool

This regression introducing during replacing port_ffi with port_buf
by 2fcce449

Linux-specific option obsolete since kernel 2.2

Wait() no longer called hence waiters not initialized. Does it make
sence to have a test for :waiters (undocumented internals)?

- Waiting on a brand new socket (neither listen nor connect called)
  completes immediately with HUP status on Linux. However on FreeBSD/osx
  it never completes.

- Attempting to connect to a port bound on a loopback interface which is
  not yet listening yield ECONNREFUSED in blocking mode on Linux. On
  FreeBSD/osx blocking connect never completes ("never" means it doesn't
  complete in a reasonable time).

- Calling shutdown() on a listening socket works in Linux but in
  FreeBSD/osx it doesn't.

Note: it was incomplete, made thing unnecessary complex and it did not
align with the CMake way (c) for crosscompilation.

Pass sysroot on OSX.
Make the code in luajit.cmake a bit more sane and straightforward.

Note: v1 of this patch was reverted due to performance regression.

Update reference to the pure php client

This reverts commit 615f0985.

This reverts commit 3010b98b.

Document UPSERT in the protocol spec.