Merge branch 'ly/load-bitmap-leakfix' into jch

Leakfix with a new and a bit invasive test.

Comments?

* ly/load-bitmap-leakfix:
  pack-bitmap: add load corrupt bitmap test
  pack-bitmap: reword comments in test_bitmap_commits()
  pack-bitmap: fix memory leak if load_bitmap() failed

diff --cc pack-bitmap.c
Simple merge

diff --cc t/t5310-pack-bitmaps.sh
Simple merge