src: remove unused symbols in node_file.cc
handle_wrap: replace unref_ field with flags_ field

Prep work for a follow-up commit that adds support for close callbacks.
handle_wrap: add close callback support
net: use close callback, not process.nextTick

Don't emit the 'close' event with process.nextTick.

Closing a handle is an operation that usually *but not always* completes
on the next tick of the event loop, hence using process.nextTick is not
reliable.

Use a proper handle close callback and emit the 'close' event from
inside the callback.

Update tests that depend on the intricacies of the old model.

Fixes #3459.
node: Add --throw-deprecation

Extremely handy when tracking down a flood of recursive nextTick warnings.
test: Pass cli flags in pummel/test-regress-GH-892
stream: Remove unnecessary nextTick usage in Writable

Fix #4928
stream: Increase highWaterMark on large reads

If the consumer of a Readable is asking for N bytes, and N > hwm,
then clearly we have set the hwm to low, and ought to increase it.

Fix #4931
stream: Remove pipeOpts.chunkSize

It's not actually necessary for backwards compatibility, isn't
used anywhere, and isn't even tested.  Better to just remove it.
stream: Remove bufferSize option

Now that highWaterMark increases when there are large reads, this
greatly reduces the number of calls necessary to _read(size), assuming
that _read actually respects the size argument.
stream: Allow strings in Readable.push/unshift

Fix #4909
stream: Raise readable high water mark in powers of 2

This prevents excessively raising the buffer level in tiny increments in
pathological cases.