Merge branch 'jc/no-git-config-in-clone'

We stopped paying attention to $GIT_CONFIG environment that points at a single configuration file from any command other than "git config" quite a while ago, but "git clone" internally set, exported, and then unexported the variable during its operation unnecessarily. * jc/no-git-config-in-clone: clone: do not export and unexport GIT_CONFIG