Build binaries using Go 1.3

Currently binaries are built using Go 1.2.2, which results
in larger binaries than those produced by newer versions of
Go. The Go source archive used for the build process is not
verified against its SHA1 hash.

Update the build-image Dockerfile to use Go 1.3 to build all
binaries, as a result binaries are now 20% - 30% smaller. The
Go source archive used for building binaries is now verified
against its SHA1 hash.
Merge pull request #633 from kelseyhightower/go1.3-build

Build binaries using Go 1.3