* io.c (set_binary_mode_with_seek_cur): reorder function qualifiers.
* test/ruby/test_io.rb (TestIO#test_pos_with_getc): added.
see [Bug #6179][ruby-core:43518]
* test/ruby/test_io.rb (TestIO#test_pos_with_getc): updated.
see [ruby-core:43550]
* io.c (static int io_fflush): add the definition.
Use it in set_binary_mode_with_seek_cur().
* io.c (set_binary_mode_with_seek_cur): refactoring to split the
content into io_unread(). Fix the possibility of buffer overflow.
* io.c (io_unread): add new implementation for Windows. Previous one
caused invalid cursor position using IO#pos with OS text mode. New
one fixes the bug.
* test/ruby/test_io_m17n.rb
(TestIO_M17N#test_pos_dont_move_cursor_position): add a test for
above bug.
[ruby-core:43497] [Bug #6179]
* io.c (io_unread): fixed memory leak. report by nagachika via IRC.
merge revision(s) 34785,35095,35098,35111,35152: [Backport #6294]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_9_3@35328 b2dd03c8-39d4-4d8f-98ff-823fe69b080e