Emit error on failed resubscribe

[gkubisa]

Normally when a subscribe callback is missing, an error event is generated on error, except for the following scenario addressed by this PR:

1. state === 'connecting'
2. subscribe() - can't subscribe in this state
3. state === 'connected'
4. _resubscribe()
5. Backend returns an error

Expected: doc.emit('error', error)
Actual: no error event

[coveralls]

Coverage increased (+0.4%) to 96.497% when pulling e97489c on Teamwork:emit-error-on-failed-resubscribe into c0e2fee on share:master.

[gkubisa]

@nateps @ericyhwang , could you provide some feedback on this PR, or merge it, if it's all good, please?

[ericyhwang]

Nate's comments, from the PR review meeting:

• The state machine on reconnecting is interesting.
• I'll have to look at the rest of the code to check for consistency.

[curran]

Suggest to close without merging due to lack of activity.