caeb67735baa8e069902e23f21d01033907c4f33 introduced a regression where
the domains stack would not be cleared after an error had been handled
by the top-level domain.

This change clears the domains stack regardless of the position of the
active domain in the stack.

PR: #9364
PR-URL: https://github.com/joyent/node/pull/9364
Reviewed-By: Trevor Norris <trev.norris@gmail.com>
Reviewed-By: Julien Gilli <julien.gilli@joyent.com>

Do not abort the process if an error is thrown from within a domain, an
error handler is setup for the domain and --abort-on-uncaught-exception
was passed on the command line.

However, if an error is thrown from within the top-level domain's error
handler and --abort-on-uncaught-exception was passed on the command
line, make the process abort.

Fixes: https://github.com/joyent/node/issues/8631
Fixes: https://github.com/joyent/node/issues/8630
PR-URL: https://github.com/joyent/node/pull/8666
Reviewed-by: Trevor Norris <trev.norris@gmail.com>

Previously if you cached process.nextTick and then require('domain')
subsequent nextTick() calls would not be caught because enqueued
functions were taking the wrong path. This keeps nextTick to a single
function reference and changes the implementation details after domain
has been required.

Even if stdio streams are opened as file streams, we should not ever try
to close them. This could be accomplished by passing `autoClose: false`
in options on their creation.

The null signal test existed, but only tested the case where the target
process existed, not when it did not exist.

Also clarified that SIGUSR1 is reserved by Node.js only for receiveing,
its not at all reserved when sending a signal with kill().

kill(pid, 'O_RDWR'), or any other node constant, "worked". I fixed this
by also checking for 'SIG'. The same as done in the isSignal() function.
Now the signal names supported by process.kill() are the same as those
supported by process.on().

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 in own file. It's important that the test remains isolated.

This reverts commit ea1cba6246a8b1784e22d076139b9244a9ff42f8.

The offending commit was intended to land on the v0.8 branch only, but
it accidentally got merged at some point.

Closes #5054.

Minor oversight in fix for #4953.