doc: fix formatting in tty.markdown

Fixes #5135.
doc: child_process: document 'error' event

Fixes #5130.
domain: fix domain callback from MakeCallback

Since _tickCallback and _tickDomainCallback were both called from
MakeCallback, it was possible for a callback to be called that required
a domain directly to _tickCallback.

The fix was to implement process.usingDomains(). This will set all
applicable functions to their domain counterparts, and set a flag in cc
to let MakeCallback know domain callbacks always need to be checked.

Added test for this case.