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/alloca.in.h

@@ -0,0 +1,65 @@
+/* Memory allocation on the stack.
+
+   Copyright (C) 1995, 1999, 2001-2004, 2006-2017 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, 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/>.
+  */
+
+/* Avoid using the symbol _ALLOCA_H here, as Bison assumes _ALLOCA_H
+   means there is a real alloca function.  */
+#ifndef _GL_ALLOCA_H
+#define _GL_ALLOCA_H
+
+/* alloca (N) returns a pointer to N bytes of memory
+   allocated on the stack, which will last until the function returns.
+   Use of alloca should be avoided:
+     - inside arguments of function calls - undefined behaviour,
+     - in inline functions - the allocation may actually last until the
+       calling function returns,
+     - for huge N (say, N >= 65536) - you never know how large (or small)
+       the stack is, and when the stack cannot fulfill the memory allocation
+       request, the program just crashes.
+ */
+
+#ifndef alloca
+# ifdef __GNUC__
+#  define alloca __builtin_alloca
+# elif defined _AIX
+#  define alloca __alloca
+# elif defined _MSC_VER
+#  include <malloc.h>
+#  define alloca _alloca
+# elif defined __DECC && defined __VMS
+#  define alloca __ALLOCA
+# elif defined __TANDEM && defined _TNS_E_TARGET
+#  ifdef  __cplusplus
+extern "C"
+#  endif
+void *_alloca (unsigned short);
+#  pragma intrinsic (_alloca)
+#  define alloca _alloca
+# elif defined __MVS__
+#  include <stdlib.h>
+# else
+#  include <stddef.h>
+#  ifdef  __cplusplus
+extern "C"
+#  endif
+void *alloca (size_t);
+# endif
+#endif
+
+#endif /* _GL_ALLOCA_H */