Recipe: setfenv with Lua 5.2.0 work3

[François Perrad <francois.perrad@...>]

With Lua 5.1, I have the following code :

    setfenv(level, M)

With Lua 5.2.0 work2, I rewrite it as following (compatible with Lua 5.1) :

    debug.setfenv(debug.getinfo(level, 'f').func, M)

Now, with Lua 5.2.0 work3, it becomes :

    if debug.setupvalue(debug.getinfo(level, 'f').func, 1, M) ~= '_ENV' then
        setfenv(level, M) -- Lua 5.1
    end

The value 1 seems magical, but I think _ENV is alway the first upvalue.

François.