Merge branch '120_diff_view'

Merge branch '120_diff_view'

* 120_diff_view: (22 commits)
  Update panels after closing the diff viewer.
  Optimization of Diff Viewer construction and destruction.
  added diff options dialog
  added save/load diffview options.
  Modified destroying of WDiff widget.
  Repaint screen after encoding change.
  Minor clean up.
  Added usage of search engine.
  added merge mechanism
  Add new section [Diff Viewer] in man and built-in help.
  Fixes of button bar handling.
  buttonbar_call(): don't handle Fx button with non-defined command.
  little fixup and optimization
  fixed display utf-8 text in 8-bit locale
  initial step to multiple encodings support and select codeset.
  Fixed segfaults in standalone diff viewer.
  src/diffviewer/ydiff.c: use GLib functions more widely.
  diffviewer: Added libmc for build depends
  Added capability to run MC as standalone diff viewer.
  src/diffviewer/ydiff.c: code indentation & cleanup.
  ...