Merge branch 'ms/fetch-prune-configuration'

Allow fetch.prune and remote.*.prune configuration variables to be set, and "git fetch" to behave as if "--prune" is given. "git fetch" that honors remote.*.prune is fine, but I wonder if we should somehow make "git push" aware of it as well. Perhaps remote.*.prune should not be just a boolean, but a 4-way "none", "push", "fetch", "both"? * ms/fetch-prune-configuration: fetch: make --prune configurable