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/lib/Makefile.am

@@ -0,0 +1,35 @@
+# Automakefile for GNU Diffutils library.
+
+# Copyright (C) 2001-2002, 2004, 2006, 2009-2013, 2015-2017 Free Software
+# Foundation, Inc.
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+AM_CFLAGS =
+BUILT_SOURCES =
+CLEANFILES =
+EXTRA_DIST =
+MOSTLYCLEANDIRS =
+MOSTLYCLEANFILES =
+MAINTAINERCLEANFILES =
+SUFFIXES =
+noinst_LIBRARIES =
+noinst_HEADERS =
+
+include gnulib.mk
+
+noinst_HEADERS += cmpbuf.h prepargs.h
+libdiffutils_a_SOURCES += cmpbuf.c prepargs.c
+
+AM_CFLAGS += $(GNULIB_WARN_CFLAGS) $(WERROR_CFLAGS)