git-clean: Display more accurate delete messages

git-clean: Display more accurate delete messages

(1) Only print out the names of the files and directories that got
    actually deleted. Also do not mention that we are not removing
    directories when the user did not ask us to do so with '-d'.
(2) Show ignore message for skipped untracked git repositories.

Consider the following repo layout:

  test.git/
    |-- tracked_dir/
    |     |-- some_tracked_file
    |     |-- some_untracked_file
    |-- tracked_file
    |-- untracked_file
    |-- untracked_foo/
    |     |-- bar/
    |     |     |-- bar.txt
    |     |-- emptydir/
    |     |-- frotz.git/
    |           |-- frotz.tx
    |-- untracked_some.git/
          |-- some.txt

Suppose the user issues 'git clean -fd' from the test.git directory.

When -d option is used and untracked directory 'foo' contains a
subdirectory 'frotz.git' that is managed by a different git repository
therefore it will not be removed.

  $ git clean -fd
  Removing tracked_dir/some_untracked_file
  Removing untracked_file
  Removing untracked_foo/
  Removing untracked_some.git/

The message displayed to the user is slightly misleading. The foo/
directory has not been removed because of foo/frotz.git still exists.
On the other hand the subdirectories 'bar' and 'emptydir' have been
deleted but they're not mentioned anywhere. Also, untracked_some.git
has not been removed either.

This behaviour is the result of the way the deletion of untracked
directories are reported. In the current implementation they are
deleted recursively but only the name of the top most directory is
printed out. The calling function does not know about any
subdirectories that could not be removed during the recursion.

Improve the way the deleted directories are reported back to
the user:
  (1) Create a recursive delete function 'remove_dirs' in builtin/clean.c
      to run in both dry_run and delete modes with the delete logic as
      follows:
        (a) Check if the current directory to be deleted is an untracked
            git repository. If it is and --force --force option is not set
            do not touch this directory, print ignore message, set dir_gone
            flag to false for the caller and return.
        (b) Otherwise for each item in current directory:
              (i)   If current directory cannot be accessed, print warning,
                    set dir_gone flag to false and return.
              (ii)  If the item is a subdirectory recurse into it,
                    check for the returned value of the dir_gone flag.
                    If the subdirectory is gone, add the name of the deleted
                    directory to a list of successfully removed items 'dels'.
                    Else set the dir_gone flag as the current directory
                    cannot be removed because we have at least one subdirectory
                    hanging around.
              (iii) If it is a file try to remove it. If success add the
                    file name to the 'dels' list, else print error and set
                    dir_gone flag to false.
        (c) After we finished deleting all items in the current directory and
            the dir_gone flag is still true, remove the directory itself.
            If failed set the dir_gone flag to false.

        (d) If the current directory cannot be deleted because the dir_gone flag
            has been set to false, print out all the successfully deleted items
            for this directory from the 'dels' list.
        (e) We're done with the current directory, return.

  (2) Modify the cmd_clean() function to:
        (a) call the recursive delete function 'remove_dirs()' for each
            topmost directory it wants to remove
        (b) check for the returned value of dir_gone flag. If it's true
            print the name of the directory as being removed.

Consider the output of the improved version:

  $ git clean -fd
  Removing tracked_dir/some_untracked_file
  Removing untracked_file
  Skipping repository untracked_foo/frotz.git
  Removing untracked_foo/bar
  Removing untracked_foo/emptydir
  Skipping repository untracked_some.git/

Now it displays only the file and directory names that got actually
deleted and shows the name of the untracked git repositories it ignored.

Reported-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
Signed-off-by: Zoltan Klinger <zoltan.klinger@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>