Simplify a bit the ontext handler.

[jails]

Just a minor refactoring to simplify the 'ontext' handler.

[fb55]

I'm not convinced this change is much of an improvement, please motivate such changes: What's the rationale? Nevertheless, I would prefer to move concatenating text sequences upstream and consider this a temporary solution, which does is job.

[jails]

Since "ontext" behave differently whether the writing is done in a stream way or not, it was just an attempt to make this "temporary solution" easier to understand since I had some troubles to get what use cases the big conditions was related to. I thought that reducing them into a single if (this._activeTextNode) { would be easier to understand but it was just a personnal taste.
Anyhow you're right, having another event like "onbody", "oncontent" or an {eager: true} option would be a way better solution.