cmd/godoc: don't crash if there's no documentation

Fixes regression introduced by CL 7860049.

R=golang-dev, kamil.kisiel, dave
CC=golang-dev
https://codereview.appspot.com/8069044
cmd/ld: when using host linker pass -r option as -rpath

R=golang-dev, daniel.morsing
CC=golang-dev
https://codereview.appspot.com/8070043
net/http: more tests, better comments, remove an allocation

Add more tests around the various orders handlers can access
and flush response headers.

Also clarify the documentation on fields of response and
chunkWriter.

While there, remove an allocation (a header clone) for simple
handlers.

benchmark                                   old ns/op    new ns/op    delta
BenchmarkServerFakeConnWithKeepAliveLite        15245        14966   -1.83%

benchmark                                  old allocs   new allocs    delta
BenchmarkServerFakeConnWithKeepAliveLite           24           23   -4.17%

benchmark                                   old bytes    new bytes    delta
BenchmarkServerFakeConnWithKeepAliveLite         1717         1668   -2.85%

R=golang-dev, gri
CC=golang-dev
https://codereview.appspot.com/8101043
cmd/godoc: cleanups

- removed gratuitous empty lines that creeped into command line output
- changed comment color to a dark green so that links don't visually melt into them
- removed some TODOs
- updated doc.go

R=golang-dev, bradfitz
CC=golang-dev
https://codereview.appspot.com/8108044
net/http: remove two more server allocations per-request

benchmark                                   old ns/op    new ns/op    delta
BenchmarkServerFakeConnWithKeepAliveLite        11031        10689   -3.10%

benchmark                                  old allocs   new allocs    delta
BenchmarkServerFakeConnWithKeepAliveLite           23           21   -8.70%

benchmark                                   old bytes    new bytes    delta
BenchmarkServerFakeConnWithKeepAliveLite         1668         1626   -2.52%

R=golang-dev, gri
CC=golang-dev
https://codereview.appspot.com/8110044
net/http: inline chunkWriter in response

A chunkWriter and a response are 1:1. Make them contiguous in
memory and save an allocation.

benchmark                                   old ns/op    new ns/op    delta
BenchmarkServerFakeConnWithKeepAliveLite        10715        10539   -1.64%

benchmark                                  old allocs   new allocs    delta
BenchmarkServerFakeConnWithKeepAliveLite           21           20   -4.76%

benchmark                                   old bytes    new bytes    delta
BenchmarkServerFakeConnWithKeepAliveLite         1626         1609   -1.05%

R=golang-dev, gri
CC=golang-dev
https://codereview.appspot.com/8114043
go/doc: fix typo in comment

R=golang-dev, bradfitz
CC=golang-dev
https://codereview.appspot.com/8113043
net/url: use strings.Index instead of a loop

We already depend on strings in this file, so use it.

Plus strings.Index will be faster than a manual loop
once issue 3751 is finished.

R=golang-dev, khr
CC=golang-dev
https://codereview.appspot.com/8116043
net/http: parse Request-Line in a function, remove an allocation

Removes another per-request allocation. Also makes the code more
readable, IMO. And more testable.

benchmark                                   old ns/op    new ns/op    delta
BenchmarkServerFakeConnWithKeepAliveLite        10539        10324   -2.04%

benchmark                                  old allocs   new allocs    delta
BenchmarkServerFakeConnWithKeepAliveLite           20           19   -5.00%

benchmark                                   old bytes    new bytes    delta
BenchmarkServerFakeConnWithKeepAliveLite         1609         1559   -3.11%

R=golang-dev, gri
CC=golang-dev
https://codereview.appspot.com/8118044
cmd/ld, runtime: restrict stack root scan to locals and arguments

Updates issue 5134

R=golang-dev, bradfitz, cshapiro, daniel.morsing, ality, iant
CC=golang-dev
https://codereview.appspot.com/8022044
cmd/godoc: provide a link from notes to source location

R=golang-dev, r
CC=golang-dev
https://codereview.appspot.com/8122043
net/http: reuse textproto.Readers; remove 2 more allocations

Saves both the textproto.Reader allocation, and its internal
scratch buffer growing.

benchmark                                   old ns/op    new ns/op    delta
BenchmarkServerFakeConnWithKeepAliveLite        10324        10149   -1.70%

benchmark                                  old allocs   new allocs    delta
BenchmarkServerFakeConnWithKeepAliveLite           19           17  -10.53%

benchmark                                   old bytes    new bytes    delta
BenchmarkServerFakeConnWithKeepAliveLite         1559         1492   -4.30%

R=golang-dev, r, gri
CC=golang-dev
https://codereview.appspot.com/8094046
cmd/ld: only pass -rdynamic to host linker on ELF target

Fixes issue 5150.

R=golang-dev, franciscossouza
CC=golang-dev
https://codereview.appspot.com/8120043
go/printer: use strings.Split instead of specialized code

With the faster strings package, the difference between
the specialized code and strings.Split is in the noise:

benchmark         old ns/op    new ns/op    delta
BenchmarkPrint     16724291     16686729   -0.22%

(Measured on a Mac Pro, 2.8GHz Quad-core Intel Xeon,
4GB 800 MHz DDR2, Mac OS X 10.8.3)

R=golang-dev, bradfitz
CC=golang-dev
https://codereview.appspot.com/8100044
net/http: unflake TestTransportConcurrency

Fixes issue 5005

R=golang-dev, r
CC=golang-dev
https://codereview.appspot.com/8127043
net: enable IPv6 tests on Windows

Also removes redundant tests that run Go 1.0 non-IPv6 support
Windows code on IPv6 enabled Windows kernels.

R=alex.brainman, golang-dev, bradfitz, dave
CC=golang-dev
https://codereview.appspot.com/7812052
net: update documentation for FileConn, FilePacketConn, FileListener

Closes the API documentation gap between platforms.

R=golang-dev, r
CC=golang-dev
https://codereview.appspot.com/8086043
net: update documentation for ListenTCP, ListenUDP

Adds the missing wildcard port assignment description to ListenUDP.
Also updates the wildcard port description on ListenTCP.

R=golang-dev, dave, r
CC=golang-dev
https://codereview.appspot.com/8063043
net: close TCPListener in example

R=golang-dev, dave
CC=golang-dev
https://codereview.appspot.com/8073044
api: remove Zone of net.IPNet from next.txt

Update issue 4234.
Update issue 4501.

R=golang-dev, dave, bradfitz
CC=golang-dev
https://codereview.appspot.com/8129043