Merge branch 'fc/remote-helper-refmap'

Allow remote-helper/fast-import based transport to rename the refs while transferring the history. * fc/remote-helper-refmap: transport-helper: remove unnecessary strbuf resets transport-helper: add support to delete branches fast-export: add support to delete refs fast-import: add support to delete refs transport-helper: add support to push symbolic refs transport-helper: add support for old:new refspec fast-export: add new --refspec option fast-export: improve argument parsing