running go1.1beta2.linux-amd64

 Just a few issues regarding bufio Scanner and zero length reads of the underlying io.Reader.

1. It is not documented that the scanner also stops on a zero length read.

2. If the underlying reader returns a zero length read with an error that is 
   not io.EOF the error is masked and Err() returns nil.
    Eg, this program will not print out the error.

package main

import (
    "bufio"
    "errors"
    "fmt"
)

type errReader struct{}

func (t *errReader) Read(p []byte) (int, error) {
    return 0, errors.New("Random Err")
}

func main() {
    scanner := bufio.NewScanner(new(errReader))
    for scanner.Scan() {
        fmt.Println(scanner.Text())
    }
    if err := scanner.Err(); err != nil {
        fmt.Println(err)
    }
}


3. I don't see in any of the other standard library readers documentation
   that they guarantee no zero length reads. If I am being paranoid, can
   I safely use them without the scan prematurely terminating before EOF?