This patch adds a new Lua module called 'pickle'. This module incorporates
former box.pack() and box.unpack() functions. These functions removed from
core because they are not needed for box anymore. This patch also removes all
box-specific formats from these functions.

(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