Merge branch 'fc/transport-helper-error-reporting'

Merge branch 'fc/transport-helper-error-reporting'

Update transport helper to report errors and maintain ref hierarchy
used to keep track of remote helper state better.

* fc/transport-helper-error-reporting:
  transport-helper: fix remote helper namespace regression
  test: remote-helper: add missing and
  t5801: "VAR=VAL shell_func args" is forbidden
  transport-helper: update remote helper namespace
  transport-helper: trivial code shuffle
  transport-helper: warn when refspec is not used
  transport-helper: clarify pushing without refspecs
  transport-helper: update refspec documentation
  transport-helper: clarify *:* refspec
  transport-helper: improve push messages
  transport-helper: mention helper name when it dies
  transport-helper: report errors properly