Implement basic support for stored functions in C/C++.

- split away struct func from struct func_def (function
object and function definition object).
- extend box.schema.func.create() to accept 'language' argument.
- move module API related cmake magic to its own file
- add test/lib to gitignore
- update to the new test-run
- add a test

added additional checks to /wal_off/snapshot_stress.test.lua

Conflicts:
	test/box/bsdsocket.result
	test/box/bsdsocket.test

Replace socket('AF_UNIX', 'SOCK_STREAM', 'ip') with
        socket('AF_UNIX', 'SOCK_STREAM', 0).

Fixes distributions with missing "ip 0 IP" line in /etc/protocols
(e.g. Arch Linux).

socket method is writable(), not writeable().

In case output is multiplexed, obuf_rollback_to_svp could
roll back to a very early  in the output buffer, since
svp is taken before a possible yield.

This is a regression introduced in the patch which
removes iproto_port from Lua calls.

Test case

*)added proper cleanup
*)minor fixes and checks

vclock_get() can return -1 in this case.
Probably introduced by 311551f9

Push a workaround for infinite loop in backtarce_foreach() when
fiber == self: do not try to print trace of the current fiber.

Conflicts:
	src/iproto_port.cc

*) fixed potentionally unsafe code:
  on memory fail there could be port->found > 0 and uninitialized port->svp

 on memory fail there could be port->reply.found > 0 and uninitialized port->svp,
 that could lead to random error after svp restoration.
*) possibly fixed OPENTAR-97