Merge remote-tracking branch 'remotes/jnsnow/tags/bitmaps-pull-request' into staging

Merge remote-tracking branch 'remotes/jnsnow/tags/bitmaps-pull-request' into staging

Pull request

# gpg: Signature made Wed 18 Mar 2020 20:23:28 GMT
# gpg:                using RSA key F9B7ABDBBCACDF95BE76CBD07DEF8106AAFC390E
# gpg: Good signature from "John Snow (John Huston) <jsnow@redhat.com>" [full]
# Primary key fingerprint: FAEB 9711 A12C F475 812F  18F2 88A9 064D 1835 61EB
#      Subkey fingerprint: F9B7 ABDB BCAC DF95 BE76  CBD0 7DEF 8106 AAFC 390E

* remotes/jnsnow/tags/bitmaps-pull-request:
  block/qcow2-bitmap: use bdrv_dirty_bitmap_next_dirty
  nbd/server: use bdrv_dirty_bitmap_next_dirty_area
  nbd/server: introduce NBDExtentArray
  block/dirty-bitmap: improve _next_dirty_area API
  block/dirty-bitmap: add _next_dirty API
  block/dirty-bitmap: switch _next_dirty_area and _next_zero to int64_t
  hbitmap: drop meta bitmaps as they are unused
  hbitmap: unpublish hbitmap_iter_skip_words
  hbitmap: move hbitmap_iter_next_word to hbitmap.c
  hbitmap: assert that we don't create bitmap larger than INT64_MAX
  build: Silence clang warning on older glib autoptr usage

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>