Merge branch 'kn/for-each-ref-skip-updates'

Merge branch 'kn/for-each-ref-skip-updates'

Code clean-up.

* kn/for-each-ref-skip-updates:
  ref-filter: use REF_ITERATOR_SEEK_SET_PREFIX instead of '1'
  t6302: add test combining '--start-after' with '--exclude'
  for-each-ref: reword the documentation for '--start-after'
  for-each-ref: fix documentation argument ordering
  ref-cache: use 'size_t' instead of int for length