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

diff --cc Documentation/git-fast-import.txt
Simple merge

diff --cc t/t5801-remote-helpers.sh
Simple merge

diff --cc transport-helper.c
index 4cfb8f3a4acc36681774e165f92de7fbd948fde5,a90094d4a3b6132a37343be093ca78e41b246ffd..84c616f180bebc730d05f306906558dd0abad2a4
--- 1/transport-helper.c
--- 2/transport-helper.c
+++ b/transport-helper.c
@@@ -897,17 -915,11 +909,19 @@@ static int push_refs_with_export(struc
        if (get_exporter(transport, &exporter, &revlist_args))
                die("Couldn't run fast-export");
  
+       string_list_clear(&revlist_args, 1);
+ 
        if (finish_command(&exporter))
                die("Error while running fast-export");
 -      push_update_refs_status(data, remote_refs, flags);
 +      if (push_update_refs_status(data, remote_refs, flags))
 +              return 1;
 +
 +      if (data->export_marks) {
 +              strbuf_addf(&buf, "%s.tmp", data->export_marks);
 +              rename(buf.buf, data->export_marks);
 +              strbuf_release(&buf);
 +      }
 +
        return 0;
  }