Log Message:
Update Go to 1.5.1.

go1.5.1 (released 2015/09/08) includes bug fixes to the compiler, assembler,
and the fmt, net/textproto, net/http, and runtime packages. See the Go 1.5.1
milestone on our issue tracker for details:
https://github.com/golang/go/issues?q=milestone%3AGo1.5.1