Merge branch 'jk/free-commit-buffer-of-skipped-commits'

The code forgot to discard unnecessary in-core commit buffer data
for commits that "git log --skip=<number>" traversed but omitted
from the output, which has been corrected.

* jk/free-commit-buffer-of-skipped-commits:
  revision: free commit buffers for skipped commits

diff --cc revision.c
Simple merge