Merge branch 'rs/commit-stack'

Code clean-up, unifying various hand-rolled "list of commit objects" and use the commit_stack API. * rs/commit-stack: commit-reach: use commit_stack commit-graph: use commit_stack commit: add commit_stack_grow() shallow: use commit_stack pack-bitmap-write: use commit_stack commit: add commit_stack_init() test-reach: use commit_stack remote: use commit_stack for src_commits remote: use commit_stack for sent_tips remote: use commit_stack for local_commits name-rev: use commit_stack midx: use commit_stack log: use commit_stack revision: export commit_stack