An intermediate step, use size0 for 'size' temporarily,
to ensure there are no compilation errors.

This is a code review of Konstantin Shulgin's branch
refactoring-tbuf.

Fix a bug in next slot calculation (creeped in with
code review fixes).

Conflicts:
	mod/box/box.m
	mod/box/index.m

Add comments.
Rewrite put_slot loop to make it *both* clear and efficient.

There is no need to check for equality in put_slot loop
once we meet first non-dirty element: a non-dirty
link indicates the end of the collision chain.

Do not move elements up the chain in put_slot loop:
we may use index in the hash/tree as tuple
id in secondary keys.

Fix a compile failiure when BFD is not installed.
Make test results execution-order independent (fiber
id depends on how many fibers were created so far).

Conflicts:
	test/box/lua.result
	test/box/lua.test

Add box.fiber.create(), box.fiber.resume(),
fiber.yield(), box.fiber.detach().

Add tests.

Makce fiber cancellation implementation
more robust and quick, so that it
is actually usable from Lua.
Debug.

Implement box.tuple.unpack(), which converts the tuple
to a list of lua atoms.

Add basic support for splice in box.update() operation.

Creating a new userdata object whenever a fiber is accessed
is inefficient and complicates fiber garbage collection:
if a fiber is referenced to by multiple userdata instances,
it's hard to know when to free it up. Implement
'memoize' pattern for fiber userdata to deal with
these two issues.

After this patch, no matter how and where from
one gets a reference to a fiber, it's the same
userdata object.

As a side effect, getting fiber identity in Lua
is also easy -- one can just directly compare two
fibers to tell whether or not they are the same.

Add fiber.cancel(), fiber.sleep(), fiber.testcancel(),
fiber.id().
Draft the fiber library interface description.