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/warn-on-use.m4

@@ -0,0 +1,47 @@
+# warn-on-use.m4 serial 5
+dnl Copyright (C) 2010-2017 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.
+
+# gl_WARN_ON_USE_PREPARE(INCLUDES, NAMES)
+# ---------------------------------------
+# For each whitespace-separated element in the list of NAMES, define
+# HAVE_RAW_DECL_name if the function has a declaration among INCLUDES
+# even after being undefined as a macro.
+#
+# See warn-on-use.h for some hints on how to poison function names, as
+# well as ideas on poisoning global variables and macros.  NAMES may
+# include global variables, but remember that only functions work with
+# _GL_WARN_ON_USE.  Typically, INCLUDES only needs to list a single
+# header, but if the replacement header pulls in other headers because
+# some systems declare functions in the wrong header, then INCLUDES
+# should do likewise.
+#
+# It is generally safe to assume declarations for functions declared
+# in the intersection of C89 and C11 (such as printf) without
+# needing gl_WARN_ON_USE_PREPARE.
+AC_DEFUN([gl_WARN_ON_USE_PREPARE],
+[
+  m4_foreach_w([gl_decl], [$2],
+    [AH_TEMPLATE([HAVE_RAW_DECL_]AS_TR_CPP(m4_defn([gl_decl])),
+      [Define to 1 if ]m4_defn([gl_decl])[ is declared even after
+       undefining macros.])])dnl
+dnl FIXME: gl_Symbol must be used unquoted until we can assume
+dnl autoconf 2.64 or newer.
+  for gl_func in m4_flatten([$2]); do
+    AS_VAR_PUSHDEF([gl_Symbol], [gl_cv_have_raw_decl_$gl_func])dnl
+    AC_CACHE_CHECK([whether $gl_func is declared without a macro],
+      gl_Symbol,
+      [AC_COMPILE_IFELSE([AC_LANG_PROGRAM([$1],
+[@%:@undef $gl_func
+  (void) $gl_func;])],
+        [AS_VAR_SET(gl_Symbol, [yes])], [AS_VAR_SET(gl_Symbol, [no])])])
+    AS_VAR_IF(gl_Symbol, [yes],
+      [AC_DEFINE_UNQUOTED(AS_TR_CPP([HAVE_RAW_DECL_$gl_func]), [1])
+       dnl shortcut - if the raw declaration exists, then set a cache
+       dnl variable to allow skipping any later AC_CHECK_DECL efforts
+       eval ac_cv_have_decl_$gl_func=yes])
+    AS_VAR_POPDEF([gl_Symbol])dnl
+  done
+])