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/malloca.m4

@@ -0,0 +1,15 @@
+# malloca.m4 serial 1
+dnl Copyright (C) 2003-2004, 2006-2007, 2009-2017 Free Software Foundation,
+dnl 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_MALLOCA],
+[
+  dnl Use the autoconf tests for alloca(), but not the AC_SUBSTed variables
+  dnl @ALLOCA@ and @LTALLOCA@.
+  dnl gl_FUNC_ALLOCA   dnl Already brought in by the module dependencies.
+  AC_REQUIRE([gl_EEMALLOC])
+  AC_REQUIRE([AC_TYPE_LONG_LONG_INT])
+])