fix JRuby display issue

JRuby with newer JVM dows not seems to flush stdout at an expected timing.
By explicitly flushing the output, the screen state is finalized before issuing win32api calls.

Author: YO4

lib/reline/io/windows.rb

@@ -3,6 +3,8 @@
 class Reline::Windows < Reline::IO
 
   attr_writer :output
+  attr_reader :jruby_p
+  alias flush_before_control? jruby_p
 
   def initialize
     @input_buf = []
@@ -32,6 +34,7 @@ def initialize
     @WaitForSingleObject = Win32API.new('kernel32', 'WaitForSingleObject', ['L', 'L'], 'L')
 
     @legacy_console = getconsolemode & ENABLE_VIRTUAL_TERMINAL_PROCESSING == 0
+    @jruby_p = RUBY_ENGINE == 'jruby'
   end
 
   def encoding
@@ -182,11 +185,6 @@ def call(*args)
     call_with_console_handle(@SetConsoleMode, mode)
   end
 
-  #if @legacy_console
-  #  setconsolemode(getconsolemode() | ENABLE_VIRTUAL_TERMINAL_PROCESSING)
-  #  @legacy_console = (getconsolemode() & ENABLE_VIRTUAL_TERMINAL_PROCESSING == 0)
-  #end
-
   def msys_tty?(io = @hConsoleInputHandle)
     # check if fd is a pipe
     if @GetFileType.call(io) != FILE_TYPE_PIPE
@@ -366,22 +364,26 @@ def get_console_screen_buffer_info
   ALTERNATIVE_CSBI = [80, 24, 0, 0, 7, 0, 0, 79, 23].freeze
 
   def get_screen_size
+    @output.flush if flush_before_control?
     width, _, _, _, _, _, top, _, bottom = get_console_screen_buffer_info || ALTERNATIVE_CSBI
     [bottom - top + 1, width]
   end
 
   def cursor_pos
+    @output.flush if flush_before_control?
     _, _, x, y, _, _, top, = get_console_screen_buffer_info || ALTERNATIVE_CSBI
     Reline::CursorPos.new(x, y - top)
   end
 
   def move_cursor_column(val)
+    @output.flush if flush_before_control?
     _, _, _, y, = get_console_screen_buffer_info
     call_with_console_handle(@SetConsoleCursorPosition, y * 65536 + val) if y
   end
 
   def move_cursor_up(val)
     if val > 0
+      @output.flush if flush_before_control?
       _, _, x, y, _, _, top, = get_console_screen_buffer_info
       return unless y
       y = (y - top) - val
@@ -394,6 +396,7 @@ def move_cursor_up(val)
 
   def move_cursor_down(val)
     if val > 0
+      @output.flush if flush_before_control?
       _, _, x, y, _, _, top, _, bottom = get_console_screen_buffer_info
       return unless y
       screen_height = bottom - top
@@ -406,6 +409,7 @@ def move_cursor_down(val)
   end
 
   def erase_after_cursor
+    @output.flush if flush_before_control?
     width, _, x, y, attributes, = get_console_screen_buffer_info
     return unless x
     written = 0.chr * 4
@@ -423,6 +427,7 @@ def scroll_down(x)
 
   def clear_screen
     if @legacy_console
+      @output.flush if flush_before_control?
       width, _, _, _, attributes, _, top, _, bottom = get_console_screen_buffer_info
       return unless width
       fill_length = width * (bottom - top + 1)