Merge branch 'ps/reftable-libgit2-cleanup'

Code clean-ups. * ps/reftable-libgit2-cleanup: refs/reftable: always reload stacks when creating lock reftable: don't second-guess errors from flock interface reftable/stack: handle outdated stacks when compacting reftable/stack: allow passing flags to `reftable_stack_add()` reftable/stack: fix compiler warning due to missing braces reftable/stack: reorder code to avoid forward declarations reftable/writer: drop Git-specific `QSORT()` macro reftable/writer: fix type used for number of records