What steps will reproduce the problem?
If possible, include a link to a program on play.golang.org.
1. With 1.1, `go get` a package from e.g. GitHub
2. With tip, `go get -u` the same package
3.

What is the expected output?
`go get -u` should finish without an error

What do you see instead?
# cd /home/dominikh/prj/go/src/github.com/kisielk/errcheck; git pull --ff-only
You are not currently on a branch. Please specify which
branch you want to merge with. See git-pull(1) for details.

    git pull <remote> <branch>

package github.com/kisielk/errcheck: exit status 1


Which compiler are you using (5g, 6g, 8g, gccgo)?


Which operating system are you using?
Linux / git version 1.8.1.5

Which version are you using?  (run 'go version')
go version devel +5af92313c1b8 Mon Aug 05 11:59:59 2013 +1000 linux/amd64

Please provide any additional information below.
https://golang.org/cl/10869046/ and
https://golang.org/cl/10907043 changed the behaviour of `go get` to
use the master branch and `git pull` instead of `git fetch` for updating.

This, however, breaks `go get -u` when the initial `go get` was done before
these changes, i.e. with the current release version of Go.

The old `go get` will result in a repository that requires `git fetch` to be
updated but the new `go get` will only attempt `git pull`. This means
that if the next version of Go includes these changes, `go get -u` will
be broken for all already installed packages that use git.