[luaposix] Return values of mkstemp

[Bernd Eggink <monoped@...>]

According to the luaposix doc, a successful call to function mkstemp() 
returns

     int open file descriptor

But I noticed that it also returns the created file name as second 
value, which is very convenient. Is it just a documentation error, in 
other words, can I rely on this behaviour, or not?

-- Bernd