(hat tip to Petr Yanovich).

A fix and a test case for gh-300: misleading error message for a
non-existing function.

First, check that a function exists. Then check access rights
to the function.

The confusion arose when trying to create a space with an
existing id.
The error message is no longer misleading.

Conflicts:
	src/lua/init.cc

* error(fmt, args)
* warn(fmt, args)
* info(fmt, args)
* debug(fmt, args)

All bultin modules can be loaded with require('modulename')
instead of require('box.modulename')

Other changes:

 * _G.box is not initialized from tarantool_lua_init() anymore
 * box.info, box.stat, box.snapshot moved to src/box/lua
 * box.coredump() => coredump()
 * box.xxx = require('box.xxx') removed from tests

Conflicts:
	test/box/protocol.test.lua
	test/box/socket.result
	test/box/socket.test.py

Conflicts:
	test/box/cfg.result

Conflicts:
	src/box/lua/schema.lua
	test/big/lua.result
	test/box/access.result
	test/box/access.test.lua
	test/box/bad_trigger.result
	test/box/bad_trigger.test.py