Merge branch 'cp/unit-test-reftable-pq'

Merge branch 'cp/unit-test-reftable-pq'

The tests for "pq" part of reftable library got rewritten to use
the unit test framework.

* cp/unit-test-reftable-pq:
  t-reftable-pq: add tests for merged_iter_pqueue_top()
  t-reftable-pq: add test for index based comparison
  t-reftable-pq: make merged_iter_pqueue_check() callable by reference
  t-reftable-pq: make merged_iter_pqueue_check() static
  t: move reftable/pq_test.c to the unit testing framework
  reftable: change the type of array indices to 'size_t' in reftable/pq.c
  reftable: remove unnecessary curly braces in reftable/pq.c