Merge branch 'ps/more-sign-compare'

More -Wsign-compare fixes.

* ps/more-sign-compare:
  sign-compare: avoid comparing ptrdiff with an int/unsigned
  commit-reach: use `size_t` to track indices when computing merge bases
  shallow: fix -Wsign-compare warnings
  builtin/log: fix remaining -Wsign-compare warnings
  builtin/log: use `size_t` to track indices
  commit-reach: use `size_t` to track indices in `get_reachable_subset()`
  commit-reach: use `size_t` to track indices in `remove_redundant()`
  commit-reach: fix type of `min_commit_date`
  commit-reach: fix index used to loop through unsigned integer
  prio-queue: fix type of `insertion_ctr`