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/sig-handler.h

@@ -0,0 +1,54 @@
+/* Convenience declarations when working with <signal.h>.
+
+   Copyright (C) 2008-2017 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/>.  */
+
+#ifndef _GL_SIG_HANDLER_H
+#define _GL_SIG_HANDLER_H
+
+#include <signal.h>
+
+#ifndef _GL_INLINE_HEADER_BEGIN
+ #error "Please include config.h first."
+#endif
+_GL_INLINE_HEADER_BEGIN
+#ifndef SIG_HANDLER_INLINE
+# define SIG_HANDLER_INLINE _GL_INLINE
+#endif
+
+/* Convenience type when working with signal handlers.  */
+typedef void (*sa_handler_t) (int);
+
+/* Return the handler of a signal, as a sa_handler_t value regardless
+   of its true type.  The resulting function can be compared to
+   special values like SIG_IGN but it is not portable to call it.  */
+SIG_HANDLER_INLINE sa_handler_t _GL_ATTRIBUTE_PURE
+get_handler (struct sigaction const *a)
+{
+#ifdef SA_SIGINFO
+  /* POSIX says that special values like SIG_IGN can only occur when
+     action.sa_flags does not contain SA_SIGINFO.  But in Linux 2.4,
+     for example, sa_sigaction and sa_handler are aliases and a signal
+     is ignored if sa_sigaction (after casting) equals SIG_IGN.  So
+     use (and cast) sa_sigaction in that case.  */
+  if (a->sa_flags & SA_SIGINFO)
+    return (sa_handler_t) a->sa_sigaction;
+#endif
+  return a->sa_handler;
+}
+
+_GL_INLINE_HEADER_END
+
+#endif /* _GL_SIG_HANDLER_H */