http: close connection on 204 and chunked encoding

This is similar to commit 2cbf458 but this time for 204 No Content
instead of 304 Not Modified responses.

When the user sends a 204 response with a Transfer-Encoding: chunked
header, suppress sending the zero chunk and force the connection to
close.
gitignore: ignore v8.log files
streams: Support objects other than Buffers

We detect for non-string and non-buffer values in onread and
turn the stream into an "objectMode" stream.

If we are in "objectMode" mode then howMuchToRead will
always return 1, state.length will always have 1 appended
to it when there is a new item and fromList always takes
the first value from the list.

This means that for object streams, the n in read(n) is
ignored and read() will always return a single value

Fixed a bug with unpipe where the pipe would break because
the flowing state was not reset to false.

Fixed a bug with sync cb(null, null) in _read which would
forget to end the readable stream
streams2: Handle sync read callbacks nicely
test: Add test for negative stream drain counter
tls: make slab buffer's size configurable

see #4636
V8: Upgrade to 3.15.11.10
V8: Reapply floating patches
npm: Upgrade to v1.2.3