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/limits-h.m4

@@ -0,0 +1,31 @@
+dnl Check whether limits.h has needed features.
+
+dnl Copyright 2016-2017 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.
+
+dnl From Paul Eggert.
+
+AC_DEFUN_ONCE([gl_LIMITS_H],
+[
+  gl_CHECK_NEXT_HEADERS([limits.h])
+
+  AC_CACHE_CHECK([whether limits.h has ULLONG_WIDTH etc.],
+    [gl_cv_header_limits_width],
+    [AC_COMPILE_IFELSE(
+       [AC_LANG_PROGRAM([[#ifndef __STDC_WANT_IEC_60559_BFP_EXT__
+                           #define __STDC_WANT_IEC_60559_BFP_EXT__ 1
+                          #endif
+                          #include <limits.h>
+                          int ullw = ULLONG_WIDTH;]])],
+       [gl_cv_header_limits_width=yes],
+       [gl_cv_header_limits_width=no])])
+  if test "$gl_cv_header_limits_width" = yes; then
+    LIMITS_H=
+  else
+    LIMITS_H=limits.h
+  fi
+  AC_SUBST([LIMITS_H])
+  AM_CONDITIONAL([GL_GENERATE_LIMITS_H], [test -n "$LIMITS_H"])
+])