Support event system in the latest IRuby

Author: mrkn

lib/matplotlib/iruby.rb

@@ -214,13 +214,24 @@ def configure_inline_support(backend)
         # Temporally monky-patching IRuby kernel to enable flushing and closing figures.
         # TODO: Make this feature a pull-request for sciruby/iruby.
         kernel = ::IRuby::Kernel.instance
-        kernel.extend HookExtension
+        kernel.extend HookExtension unless kernel.respond_to?(:events)
         if backend == GUI_BACKEND_MAP[:inline]
-          kernel.register_event(:post_execute, method(:flush_figures))
+          if kernel.respond_to?(:register_event)
+            kernel.register_event(:post_execute, method(:flush_figures))
+          else
+            @post_execute_func = kernel.events.register(:post_execute, &method(:flush_figures))
+          end
+
           # TODO: save original rcParams and overwrite rcParams with IRuby-specific configuration
           new_backend_name = :inline
         else
-          kernel.unregister_event(:post_execute, method(:flush_figures))
+          if kernel.respond_to?(:unregister_event)
+            kernel.unregister_event(:post_execute, method(:flush_figures))
+          elsif @post_execute_func
+            kernel.events.unregister(:post_execute, @post_execute_func)
+            @post_execute_func = nil
+          end
+
           # TODO: restore saved original rcParams
           new_backend_name = :not_inline
         end