Merge branch 'jc/grep'

Merge branch 'jc/grep'

* jc/grep: (22 commits)
  Fix silly typo in new builtin grep
  builtin-grep: unparse more command line options.
  builtin-grep: use external grep when we can take advantage of it
  builtin-grep: -F (--fixed-strings)
  builtin-grep: -w fix
  builtin-grep: typofix
  builtin-grep: tighten argument parsing.
  builtin-grep: documentation
  Teach -f <file> option to builtin-grep.
  builtin-grep: -L (--files-without-match).
  builtin-grep: binary files -a and -I
  builtin-grep: terminate correctly at EOF
  builtin-grep: tighten path wildcard vs tree traversal.
  builtin-grep: support -w (--word-regexp).
  builtin-grep: support -c (--count).
  builtin-grep: allow more than one patterns.
  builtin-grep: allow -<n> and -[ABC]<n> notation for context lines.
  builtin-grep: printf %.*s length is int, not ptrdiff_t.
  builtin-grep: do not use setup_revisions()
  builtin-grep: support '-l' option.
  ...