D7: editor multi-cursor support

Add secondary_cursors field to Editor with insert_char_multi,
delete_back_multi, delete_forward_multi methods. Right-to-left
processing ensures position shifts don't corrupt earlier insertions.

7 new tests: add/clear, all_positions, insert, delete_back,
delete_forward, unicode, duplicate-add.

local/recipes/tools/diffutils/source/THANKS

@@ -0,0 +1,23 @@
+Thanks to all the following for their contributions to GNU diffutils:
+
+Thomas Bushnell, BSG  <tb@becket.net>
+Wayne Davison  <wayne@opencoder.net>
+Ulrich Drepper  <drepper@redhat.com>
+Paul Eggert  <eggert@cs.ucla.edu>
+Jay Fenlason  <fenlason@redhat.com>
+John Gilmore  <gnu@toad.com>
+Torbjorn Granlund  <tege@swox.com>
+Mike Haertel  <mike@ichips.intel.com>
+Bruno Haible  <haible@clisp.org>
+Chris Hanson <cph@gnu.org>
+Jim Kingdon  <kingdon@panix.com>
+Tom Lord  <lord@gnu.org>
+David J. MacKenzie  <djm@gnu.org>
+Roland McGrath  <roland@redhat.com>
+Jim Meyering  <jim@meyering.net>
+Gene Myers  <gene@eecs.berkeley.edu>
+Randy Smith  <randy@gnu.org>
+Richard Stallman  <rms@gnu.org>
+Leonard H. Tower Jr.  <tower@art.net>
+Larry Wall  <larry@wall.org>
+Eli Zaretskii  <eliz@gnu.org>