repl: surrogate pair upsets repl / terminal

```
$ out/Release/iojs
> Buffer([0,0xD8,0,0xDC]).toString('utf16le')
'
# screen freezes
```

The REPL still accepts input but no longer echoes it.  Typing in `process.exit()` cleanly shuts down the process but the terminal isn't reset, leaving it in an unusable state until you run reset(1).
