"git grep" has been taught to optionally recurse into submodules.

* bw/grep-recurse-submodules:
  grep: search history of moved submodules
  grep: enable recurse-submodules to work on <tree> objects
  grep: optionally recurse into submodules
  grep: add submodules as a grep source type
  submodules: load gitmodules file from commit sha1
  submodules: add helper to determine if a submodule is initialized
  submodules: add helper to determine if a submodule is populated
  real_path: canonicalize directory separators in root parts
  real_path: have callers use real_pathdup and strbuf_realpath
  real_path: create real_pathdup
  real_path: convert real_path_internal to strbuf_realpath
  real_path: resolve symlinks by hand