stream: Pass 'buffer' encoding to decoded writables

Since the encoding is no longer relevant once it is decoded to a Buffer,
it is confusing and incorrect to pass the encoding as 'utf8' or whatever
in those cases.

Closes #6119
doc: Adjust util stability index to 'API Frozen'

Closes #6087
stream: check _events before _events.error

This fixes the regression introduced by 5458079, which breaks the
net/net-pipe benchmark script.

Closes #6145
benchmark: Support passing v8 flags to benchmarks

The better to test --use-strict effects on performance.

(Spoiler: it has no measurable effect on performance.)
benchmark: Fix execArgv handling

Bug in 01f3b46 causes the same benchmark to be run repeatedly.

Not so useful for the compare scripts.
doc: fix writable.write link
2013.09.04, Version 0.10.18 (Stable)

* uv: Upgrade to v0.10.15

* stream: Don't crash on unset _events property (isaacs)

* stream: Pass 'buffer' encoding with decoded writable chunks (isaacs)
Merge branch 'v0.10.18-release' into v0.10
Now working on 0.10.19
blog: Post for v0.10.18
blog: Post for v0.11.7
uv: upgrade to v0.10.16
stream: objectMode transforms allow falsey values

Closes #6183
npm: upgrade to v1.3.10