Merge branch 'jn/grep-open'

Merge branch 'jn/grep-open'

* jn/grep-open:
  t/t7811-grep-open.sh: remove broken/redundant creation of fake "less" script
  t/t7811-grep-open.sh: ensure fake "less" is made executable
  t/lib-pager.sh: remove unnecessary '^' from 'expr' regular expression
  grep -O: allow optional argument specifying the pager (or editor)
  grep: Add the option '--open-files-in-pager'
  Unify code paths of threaded greps
  grep: refactor grep_objects loop into its own function

Conflicts:
	t/t7006-pager.sh