On the fsfs-format7 branch: Introduce a libsvn_subr API for priority queues.
We will soon use it in the new FSFS pack code.

* subversion/include/svn_sorts.h
  (svn__priority_queue_t): declare new data type
  (svn__priority_queue_create,
   svn__priority_queue_size,
   svn__priority_queue_peek,
   svn__priority_queue_pop,
   svn__priority_queue_push): declare new API functions

* subversion/libsvn_subr/sorts.c
  (svn__priority_queue_t): define data type
  (heap_is_less,
   heap_swap,
   heap_bubble_down,
   heap_bubble_up): new utility functions
  (svn__priority_queue_create,
   svn__priority_queue_size,
   svn__priority_queue_peek,
   svn__priority_queue_pop,
   svn__priority_queue_push): implement new API


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/fsfs-format7@1460579 13f79535-47bb-0310-9956-ffa450edef68