Multiple "waiting for unsupported file type" when compiled with go1.9beta2

[xiaq]

When compiled with go1.9beta2, typing any character in Elvish will cause a lot of these errors to be printed:

reader error: read /dev/stdin: waiting for unsupported file type

[tw4452852]

This issue due to golang/go#18507, after this, reading on a nonblocking file won't return EAGAIN any more. There are two ways to fix this issue:

1. use syscall.Read to read file directly instead of *File.Read
2. I have just propose a patch in os: reading on nonblocking stdin causes "waiting for unsupported file type" error golang/go#20915, it will keep the compatibility.

[xiaq]

@tw4452852 Thank you! :) For now let's wait a while and hope your patch gets accepted.

[tw4452852]

This issue should be fixed by golang/go@26f0a7a