crypto/x509: add function to marshal EC private keys.

This complements the parsing function that we already have.

R=golang-dev, r
CC=golang-dev
https://codereview.appspot.com/10426043
cmd/go: put the coverage information on the summary line.
Output now:
ok  	crypto/aes	0.060s	coverage: 89.8% of statements
ok  	crypto/des	0.074s	coverage: 92.2% of statements
ok  	crypto/dsa	0.056s	coverage: 34.5% of statements
ok  	crypto/ecdsa	0.058s	coverage: 86.8% of statements
ok  	crypto/elliptic	0.039s	coverage: 94.6% of statements
ok  	crypto/hmac	0.037s	coverage: 93.5% of statements
ok  	crypto/md5	0.031s	coverage: 96.2% of statements
ok  	crypto/rand	0.074s	coverage: 9.9% of statements
ok  	crypto/rc4	0.090s	coverage: 66.7% of statements
ok  	crypto/rsa	0.253s	coverage: 83.5% of statements

R=rsc, adg
CC=golang-dev
https://codereview.appspot.com/10413044
all: fix shadowing bugs found by go tool vet -shadow

R=golang-dev, bradfitz
CC=golang-dev
https://codereview.appspot.com/10328044
net/http: fix confusing shadowing in ProxyFromEnvironment

The old code worked, somewhat on accident, but was confusing,
and had a useless assignment to the inner err. It worked
because url.Parse parses just about anything, so the outer err
was always nil, so it always fell through to the bottom return
statement, even without the "err = nil" line.

Instead, just have two return statements, and add a comment.

R=golang-dev, r
CC=golang-dev
https://codereview.appspot.com/10448044
doc: update gccgo docs

R=golang-dev, r
CC=golang-dev
https://codereview.appspot.com/10401046
all: excise some warts found by vet -shadow
These are not erroneous, just poor or confusing.

R=golang-dev, bradfitz
CC=golang-dev
https://codereview.appspot.com/10448043
all: avoid leaking fds during tests

trivial: it is not a serious problem to leak a fd in a short lived process, but it was obscuring my investigation of issue 5593.

R=golang-dev, iant, bradfitz
CC=golang-dev
https://codereview.appspot.com/10391043