net/http: fix a bunch of test leaks

And one real leak in TimeoutHandler.

Fixes issue 4821

R=golang-dev, adg
CC=golang-dev
https://codereview.appspot.com/7369056
sort: add an example showing sorting struct by different keys

R=golang-dev, dsymonds
CC=golang-dev
https://codereview.appspot.com/7376058