Iota doesn't introduce an error message if used inside var declaration

<pre>package main

import &quot;fmt&quot;

var (
    a = iota
    b = iota
    c = iota
)

func main() {
    fmt.Println(a, b, c)
}

// Go compiler version: b84e614e2516 weekly/weekly.2011-03-28
// Compiler successfully compiles this code and the resulting binary prints:
// 0 0 0
// 
// Is it a bug? or an undocumented compiler extension?</pre>
