Merge branch 'ab/only-single-progress-at-once'

Merge branch 'ab/only-single-progress-at-once'

Further tweaks on progress API.

* ab/only-single-progress-at-once:
  pack-bitmap-write.c: don't return without stop_progress()
  progress API: unify stop_progress{,_msg}(), fix trace2 bug
  progress.c: refactor stop_progress{,_msg}() to use helpers
  progress.c: use dereferenced "progress" variable, not "(*p_progress)"
  progress.h: format and be consistent with progress.c naming
  progress.c tests: test some invalid usage
  progress.c tests: make start/stop commands on stdin
  progress.c test helper: add missing braces
  leak tests: fix a memory leak in "test-progress" helper