Increases the grep factor. Makes it easier to harmonize type checks
across the code base.

If a transform stream has objectMode = true, it should
allow falsey values other than (null) like 0, false, ''.

null is reserved to indicate stream eof but other falsey
values should flow through properly.

Conflicts:
	AUTHORS
	ChangeLog
	deps/uv/ChangeLog
	deps/uv/config-unix.mk
	deps/uv/src/unix/stream.c
	deps/uv/src/version.c
	deps/uv/uv.gyp
	src/node.cc
	src/node_buffer.cc
	src/node_crypto.cc
	src/node_version.h
	src/stream_wrap.cc
	src/stream_wrap.h

If there is an encoding, and we do 'stream.push(chunk, enc)', and the
encoding argument matches the stated encoding, then we're converting from
a string, to a buffer, and then back to a string.  Of course, this is a
completely pointless bit of work, so it's best to avoid it when we know
that we can do so safely.

In synchronous Writable streams (where the _write cb is called on the
current tick), the 'finish' event (and thus the end() callback) can in
some cases be called before all the write() callbacks are called.

Use a counter, and have stream.Transform rely on the 'prefinish' event
instead of the 'finish' event.

This has zero effect on most streams, but it corrects an edge case and
makes it perform more deterministically, which is a Good Thing.

The stall is exposed in the test, though the test itself asserts before
it stalls.

The test is constructed to replicate the stalling state of a complex
Passthrough usecase since I was not able to reliable trigger the stall.

Some of the preconditions for triggering the stall are:
  * rs.length >= rs.highWaterMark
  * !rs.needReadable
  * _transform() handler that can return empty transforms
  * multiple sync write() calls

Combined this can trigger a case where rs.reading is not cleared when
further progress requires this. The fix is to always clear rs.reading.