Conflicts:
	test/box/configuration.result
	test/box/configuration.test

A dead fiber could get reused prematurely or garbage collected twice.

This was because __gc could get invoked way after the fiber has
finished and reused for a different coroutine.

The fix is to always access fibers in Lua by fiber id.

Fix a hang on box.fiber.resume() of an attached fiber which gets
cancelled.
When the child fiber got cancelled before detach, the parent
never was woken up, and would hang forever.
Wake up the parent, and, in the parent, do not try to access
a dead fiber.

This patch limits maximum recursion depth for luaL_packsize and luaL_packvalue
functions to 16 nested tables. This check is needed to prevent a crash
on recursive Lua tables.

This patch adds lua_checkfield function - a wrapper for lua_tofield that raises
an error if Lua type can not be converted to lua_field structure. The function
should be used instead of lua_tofield in all bindings where custom types are not
supported.