Merge branch 'np/delta'

Merge branch 'np/delta'

* np/delta:
  builtin-pack-objects.c: avoid bogus gcc warnings
  threaded delta search: proper locking for cache accounting
  threaded delta search: add pack.threads config variable
  fix threaded delta search locking
  threaded delta search: specify number of threads at run time
  threaded delta search: better chunck split point
  threaded delta search: refine work allocation
  basic threaded delta search
  rearrange delta search progress reporting
  localize window memory usage accounting
  straighten the list of objects to deltify