tree 43507004a29edff28a41f46b009637b9be28e916
parent 5b65ac25780cc4c18c965e3202e2e882bd25d941
author Patrick Steinhardt <ps@pks.im> 1491322725 +0200
committer Patrick Steinhardt <ps@pks.im> 1491392971 +0200

repository: set error message if trying to set HEAD to a checked out one

If trying to set the HEAD of a repository to another reference, we have
to check whether this reference is already checked out in another linked
work tree. If it is, we will refuse setting the HEAD and return an
error, but do not set a meaningful error message. Add one.