The string "(null)" used for non-collectable values must be printed as a
string, not as a pointer. (Bug introduced in commit e0cbaa50fa7).

ISO C states that standard library functions should not be called
with NULL arguments, unless stated otherwise. 'sprintf' does not
state otherwise, and it doesn't hurt to be on the safe side.

That macro is applied to float attributes, not to limits.

In 'str__dump', the call to 'lua_dump' assumes the function is on the
top of the stack, but the manual allows 'luaL_buffinit' to push stuff
on the stack (although the current implementation does not).  So, the
call to 'luaL_buffinit' must come after the call to 'lua_dump'.

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'.

As an example, 'print(string.format("%.99f", 1e70))' may have a
lot of garbage after the number.

The old test to ensure that 'string.format("%.99f", n)' was not too
large, 'fabs(n) < 1e100', assumes that the number will fit in the 99
bytes; but the 99 is not the space for the number, it is the added
extra zeros.  The option worked for smaller numbers because of the
extra space added to MAX_ITEM.

The result of "string.format("%.99f", -1e308) is 410 characters long,
but all other formats have much smaller limits (at most 99 plus a fex
extras). This commit avoids 'string.format' asking for a buffer
~400 chars large when ~100 will do.