Several details in code (e.g., moving a variable to the most inner
scope that encloses its uses), comments, parameter names, extra tests.

The macro 'luaL_pushfail' documents all places in the standard libraries
that return nil to signal some kind of failure. It is defined as
'lua_pushnil'. The manual also got a notation (@fail) to document those
returns. The tests were changed to be agnostic regarding whether 'fail'
is 'nil' or 'false'.

Attributes changed to posfixed ('x <const>', instead of '<const> x'),
and "toclose" renamed to "close". Posfixed attributes seem to make it
clearer that it applies to only one variable when there are multiple
variables.

A call to 'math.randomseed()' returns the two components of the seed
it set, so that they can be used to set that same seed again.

Local constant variables initialized with compile-time constants
are optimized away from the code.

A variable can be declared const, which means it cannot be assigned to,
with the syntax 'local <const> name = exp'.

When called with no arguments, 'math.randomseed' uses time and ASLR
to generate a somewhat random seed. the initial seed when Lua starts
is generated this way.

The call 'math.rand()' converts the higher bits of the internal unsigned
integer random to a float, instead of its lower bits. That ensures that
Lua compiled with different float precisions always generates equal (up
to the available precision) random numbers when given the same seed.