Revert "lua: fix tuple cdata collecting"

This reverts commit 022a3c50.

According to FFI documentation [1], ffi.cast() creates a new object for
the given type and initializes it with the given value. So setting a
finalizer for a tuple before casting it to const_tuple_ref_t is totally
wrong as it allows the Lua interpreter to invoke the finalizer as soon
as the cast is complete. That said, we must revert the commit that
swapped ffi.cast and ffi.gc order in tuple_bless() and reopen the issue
it intended to fix - see #3751 - no wonder it improved the garbage
collector performance as it basically made all tuples collectable right
from the moment they are blessed.

To make sure we won't step on the same issue again in future, let's also
add a relevant test case.

[1] http://luajit.org/ext_ffi_api.html

Closes #3902