The explanation includes the limit case of maxinteger being a border.
It also avoids the term "natural", which might include large floats
with natural values.

Warnings with clang when using long double for Lua floats.

'os.exit' can call lua_close again, separating new finalizers
created after all previous finalizers were already separated.

correction in macro for hard tests + type in comment

The call to 'checkstackGC' can run finalizers, which will find an
inconsistent CallInfo, as 'ci' is half updated at the point of call.

The flag CIST_FIN does not mark a finalizer, but the function that was
running when the finalizer was called. (So, the function did not call
the finalizer, but it looks that way in the stack.)

As the GC is not reentrant, finalizers should not be able to invoke it.

Handle values in table keys as the special cases they are, and not
the other way around.