Doc: explicit lua_open required

["Ashley Fryer" <lua@...>]

( I'm upgrading from 3.1 so disregard if this is old news )...

It should be documented that the behavior of the standard library "open"
functions has changed.  In previous versions of Lua, a call to:

    iolib_open();
    strlib_open();
    mathlib_open();

would implicitly call lua_open.  In 4.0 alpha, the functions:

    lua_iolibopen();
    lua_strlibopen();
    lua_mathlibopen();

do not call lua_open.  In fact, these functions assume that lua_open was
already called and attempt to dereference a null lua_state pointer, which
results in a memory exception.  Since this is a case where previously valid
code crashes, it should probably be documented.

Other than the issues noted, the new version is working flawlessly in VC6.
Congratulations on a great job!

ashley