I have been running this patch inside Google against Go 1.6 for the last month.

The new tests will probably break the builders but let's see
exactly how they break.

Change-Id: Ia65cf7d3faecffeeb4b06e9b80875c0e57d86d9e
Reviewed-on: https://go-review.googlesource.com/23452Reviewed-by: Ian Lance Taylor <iant@golang.org>