join node emits incorrect data when script disabled

While trying to come up with a solution for https://groups.google.com/forum/#!topic/influxdb/sPWnPkr8pxU I noticed that when a script is disabled, a `join` node can emit incorrect data. For example:

```
var data = stream
|from().measurement('system').groupBy('host')
|stats(200ms).align()
|difference('emitted').as('emitted')

var data_crit = data
|window().period(500ms).every(1u)
|sum('emitted').as('emittedsum')

data
|join(data_crit).as('warn','crit').tolerance(200ms).fill(0)
|log()
```

when the above script is run, and fed data, and then disabled, the following is the result:

```
[deadnode:log9] 2016/09/13 13:12:30 I! {stats host=foo {false [host]} map[host:foo] map[warn.emitted:1 crit.emittedsum:5] 2016-09-13 17:12:30 +0000 UTC}
[deadnode:log9] 2016/09/13 13:12:30 I! {stats host=foo {false [host]} map[host:foo] map[warn.emitted:2 crit.emittedsum:5] 2016-09-13 17:12:30.2 +0000 UTC}
[deadnode:log9] 2016/09/13 13:12:30 I! {stats host=foo {false [host]} map[host:foo] map[warn.emitted:2 crit.emittedsum:5] 2016-09-13 17:12:30.4 +0000 UTC}
[deadnode:log9] 2016/09/13 13:12:30 I! {stats host=foo {false [host]} map[host:foo] map[warn.emitted:1 crit.emitted:0] 2016-09-13 17:12:30.6 +0000 UTC}
```

Notice that last line, how it has `crit.emitted`. This field shouldn't exist. I don't know where it's coming from. And the field that should exist, `crit.emittedsum`, does not.

This is with a kapacitor build from eccff59 (current master)

Start by running the provided Kapacitor script with the task disabled and inspect the join node's emitted fields, especially the final record. Trace the join node's handling of the warn and crit streams, then verify that disabled-script output retains crit.emittedsum and does not emit crit.emitted.

Written by the indexing model from the issue text.