Log Message:
Update dirdiff to 2.1.
Patch applied by Martin Wilke via PR 34432.

What's new in dirdiff-2.1.
--------------------------

* The diff display window can now display 3-way, 4-way and 5-way diffs
  as well as the normal 2-way diffs.  When a line is identified as
  coming from multiple files, most of it will be colored for the
  newest of those files, and extra colored bars at the left of the
  line will identify which other files it is in.

* You can now modify the diff display interactively (for example, to
  make it more understandable).  You can use the middle mouse button
  to drag the blue separator bars to expose more context, or drag
  colored diff lines up and down (the movement is constrained so as to
  not alter the meaning of the diff).  Dragging context lines splits
  them into colored diff lines.

* There is now a menu on the diff display window for generating
  patches embodying the changes that could be made with the merge
  menu.  That is, the diff lines that are checked in the diff viewer
  will be made into - and + lines in the generated patch.

* The BitKeeper integration feature has been removed.  I plan to add
  generic features for integration with arbitrary SCM systems in
  future.

What was new in dirdiff-2.0.
----------------------------

* Some great new features from Dorothy Robinson:

  - A dialog box for choosing the directories to be diffed, if dirdiff
    is invoked without specifying any directories or files on the
    command line.

  - Colored icons instead of squares in the file list window.

  - Colored icons in the Diff and Copy/Del menus (provided you are
    using Tk 8.4 or later).

  - Modifications so dirdiff can be used under Windows.

  - A color key showing the ordering of the colors.

  - Use of two-level menus for the Diff, Copy/Del and Patch menus (the
    Diff and Copy/Del menus use two levels only when there are
    sufficient alternatives for it to make things simpler).

  - A filename search function using the filename bar in the file list
    window.

  - Options to allow the user to select external diff and file viewer
    programs.

* There is now a mode for ignoring files in a directory if they match
  any of the patterns listed in the .cvsignore in that directory.
  This is invoked with the -C command-line option or by choosing the
  "Ignore files in .cvsignore" option in the Options menu.

* Some users have requested a mode in which, when a directory exists
  in one tree but not another, dirdiff display the files in that
  directory as existing in the one tree but not the other (rather than
  displaying just a single line for the directory).  This mode is
  enabled by choosing the "Show files that aren't in some dirs" option
  in the Options menu.

* Trees can now be marked as "read-only" in the Options menu.  This
  means that menu options that would modify those trees (in the
  Copy/Del, Touch and Merge menus) will not be offered.

* Files can be added to the excluded file list by selecting them and
  choosing "Exclude selection" under the File menu.

* Changes to the "Underline tabs" mode now take effect immediately.