undo CL 101330053 / c19c9a063fe8

sync.Pool is not supposed to be used everywhere, but is
a last resort.

««« original CL description
strings: use sync.Pool to cache buffer

benchmark                         old ns/op    new ns/op    delta
BenchmarkByteReplacerWriteString       3596         3094  -13.96%

benchmark                        old allocs   new allocs    delta
BenchmarkByteReplacerWriteString          1            0  -100.00%

LGTM=dvyukov
R=bradfitz, dave, dvyukov
CC=golang-codereviews
https://codereview.appspot.com/101330053
»»»

LGTM=dave
R=r, dave
CC=golang-codereviews
https://codereview.appspot.com/102610043
image/png: remove unnecessary function call

paeth(0, x, 0) == x for any uint8 value.

LGTM=nigeltao
R=golang-codereviews, bradfitz, nigeltao
CC=golang-codereviews
https://codereview.appspot.com/105290049

Committer: Nigel Tao <nigeltao@golang.org>
syscall: don't display syscall prototype lines on godoc

LGTM=dave
R=golang-codereviews, dave
CC=golang-codereviews
https://codereview.appspot.com/110020050
syscall: consolidate, simplify socket options for Unix-like systems

Also exposes common socket option functions on Solaris.

Update issue 7174
Update issue 7175

LGTM=aram
R=golang-codereviews, aram
CC=golang-codereviews
https://codereview.appspot.com/107280044