Merge branch 'jk/rev-list-count-with-bitmap' into maint

Merge branch 'jk/rev-list-count-with-bitmap' into maint

"git rev-list --count" whose walk-length is limited with "-n"
option did not work well with the counting optimized to look at the
bitmap index.

* jk/rev-list-count-with-bitmap:
  rev-list: disable bitmaps when "-n" is used with listing objects
  rev-list: "adjust" results of "--count --use-bitmap-index -n"