.writable/.readable are not updated

[mscdex]

Yes I know that these are supposedly "legacy" properties, but setting them to true and never updating them is a bug IMHO.

How else are we supposed to know if any stream has ended/finished without peering into the private _*ableState properties? For example, if you have a function that takes in a Readable stream. If the stream has already ended, it's not like you can attach an end event handler or anything.

[isaacs]

I agree, if the fields are there, they may as well be updated when they change so that they're not lying.

Unless any others provide reasonable objections, patch welcome.

[mscdex]

PR is at nodejs/node#1217