(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

Conflicts:
	test/box/misc.result

This patch renames space.n to space.id

Don't use sprintf/strncpy - they are unsafe from secure programming POV.
Remove trailing spaces. Use one empty line between function
definitions, not two. Put header guards before the licence, be nice
to the preprocessor. Put the main header file first in the implementation
file, this automatically checks that the header is self-sufficient.
Add comments. We don't use spaces before/after ( ) braces.

Weed out word "arity" and use "field_count" instead: in
variable names, error messages, tests, constants.

Consistently use parts to refer to parts of a multipart key definition.