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/getpagesize.m4

@@ -0,0 +1,32 @@
+# getpagesize.m4 serial 9
+dnl Copyright (C) 2002, 2004-2005, 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_FUNC_GETPAGESIZE],
+[
+  AC_REQUIRE([gl_UNISTD_H_DEFAULTS])
+  AC_REQUIRE([AC_CANONICAL_HOST])
+  AC_CHECK_FUNCS([getpagesize])
+  if test $ac_cv_func_getpagesize = no; then
+    HAVE_GETPAGESIZE=0
+    AC_CHECK_HEADERS([OS.h])
+    if test $ac_cv_header_OS_h = yes; then
+      HAVE_OS_H=1
+    fi
+    AC_CHECK_HEADERS([sys/param.h])
+    if test $ac_cv_header_sys_param_h = yes; then
+      HAVE_SYS_PARAM_H=1
+    fi
+  fi
+  case "$host_os" in
+    mingw*)
+      REPLACE_GETPAGESIZE=1
+      ;;
+  esac
+  dnl Also check whether it's declared.
+  dnl mingw has getpagesize() in libgcc.a but doesn't declare it.
+  AC_CHECK_DECL([getpagesize], , [HAVE_DECL_GETPAGESIZE=0])
+])