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/m4/strtoumax.m4

@@ -0,0 +1,28 @@
+# strtoumax.m4 serial 12
+dnl Copyright (C) 2002-2004, 2006, 2009-2017 Free Software Foundation, Inc.
+dnl This file is free software; the Free Software Foundation
+dnl gives unlimited permission to copy and/or distribute it,
+dnl with or without modifications, as long as this notice is preserved.
+
+AC_DEFUN([gl_FUNC_STRTOUMAX],
+[
+  AC_REQUIRE([gl_INTTYPES_H_DEFAULTS])
+
+  dnl On OSF/1 5.1 with cc, this function is declared but not defined.
+  AC_CHECK_FUNCS_ONCE([strtoumax])
+  AC_CHECK_DECLS_ONCE([strtoumax])
+  if test "$ac_cv_have_decl_strtoumax" = yes; then
+    if test "$ac_cv_func_strtoumax" != yes; then
+      # HP-UX 11.11 has "#define strtoimax(...) ..." but no function.
+      REPLACE_STRTOUMAX=1
+    fi
+  else
+    HAVE_DECL_STRTOUMAX=0
+  fi
+])
+
+# Prerequisites of lib/strtoumax.c.
+AC_DEFUN([gl_PREREQ_STRTOUMAX], [
+  AC_CHECK_DECLS([strtoull])
+  AC_REQUIRE([AC_TYPE_UNSIGNED_LONG_LONG_INT])
+])