stream: pause cancels pending resumes

In looking into fixing [this jenkins error](http://jenkins.nodejs.org/job/nodejs-master/DESTCPU=ia32,label=smartos/1298/tapTestReport/simple.tap-564/), I ran into a situation where v0.11 differs from v0.10 stream behavior:

```bash
$  node -e 'setInterval(process.stdout.write.bind(process.stdout, "beep"), 100)' | node test/simple/test-stdin-pause-resume-sync.js
```

In v0.10, the above will eventually error out with EPIPE. In v0.11, it will hang forever (with `NODE_DEBUG=stream,net`, it produces [this output](https://gist.github.com/chrisdickinson/c29ba12b7f1a4fcc3539/)).

This fixes that change in behavior (and may have the side effect of fixing the jenkins bug, though I was unable to reproduce that bug on smartos itself). The problem was that `resume` defers its actual work with `process.nextTick`, between which time `pause` may be called. In the stdin case, `resume` triggers a `read`, which `readStart`'s the handle, and the process is kept open by a continuing `maybeReadMore` since the handle is open and data continues to flow in.