user can throw an exception with choised code.

Conflicts:
	third_party/README

Conflicts:
	third_party/README

Inline bio_socket_close().
Don't allow connect/bind on a non-empty socket:this is error-prone.
Don't allow connect/bind on a socket which
is already connected/bound/used for something else.
This is error-prone.
Move bind_addrinfo to evio layer.
Don't create iobuf without need. In close(), set iobuf to NULL.
Timeouts are not exceptions. Merge _timeout and other calls in coio.

Do not throw exceptions from coeio_connect_addrinfo() if timeout.
Rename box.io to box.socket.

When make test is run with gcov, coverage output files are
created. On the second run, when they are already there,
the server fails to start.

There is already a test for this, but it is only possible
to repeat the condition for a bug in client/server testing (not localhost).

https://bugs.launchpad.net/tarantool/+bug/1090381