Merge branch 'ab/usage-die-message'

Code clean-up to hide vreportf() from public API.

* ab/usage-die-message:
  config API: use get_error_routine(), not vreportf()
  usage.c + gc: add and use a die_message_errno()
  gc: return from cmd_gc(), don't call exit()
  usage.c API users: use die_message() for error() + exit 128
  usage.c API users: use die_message() for "fatal :" + exit 128
  usage.c: add a die_message() routine

diff --cc builtin/notes.c
Simple merge

diff --cc git-compat-util.h
Simple merge

diff --cc http-backend.c
Simple merge

diff --cc parse-options.c
Simple merge

diff --cc run-command.c
Simple merge