Implement functions which change their effective
user id ot the one of the definer during execution.

Conflicts:
	src/box/lua/box_net.lua

Conflicts:
	src/lua/bsdsocket.cc
	src/lua/bsdsocket.lua
	test/box/bsdsocket.result
	test/box/bsdsocket.test

Fixes compatibility with third-party modules.

This patch also adds argument checking to all socket methods.

1. snapshot_save calls snapshot_space
2. snapshot_space uses index->initIterator()
3. initIterator() doesn't work until endBuild() is called
4. index->endBuild() is called by space_end_recover_snapshot()
   *after* snapshot_save()
=> Replica doesn't save some tuples into snapshot on JOIN

This patch changes space_end_recover_snapshot() order.

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

(fix httpd log messages)