Merge branch 'pc/submodule-helper-foreach'

The bulk of "git submodule foreach" has been rewritten in C. * pc/submodule-helper-foreach: submodule: port submodule subcommand 'foreach' from shell to C submodule foreach: document variable '$displaypath' submodule foreach: document '$sm_path' instead of '$path' submodule foreach: correct '$path' in nested submodules from a subdirectory