Merge branch 'ps/reftable-libgit2-cleanup'

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  reftable/stack: handle outdated stacks when compacting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