* include/ruby/encoding.h (rb_enc_right_char_head): ditto.
* io.c (appendline): does multibyte RS search in the function.
* io.c (prepare_getline_args): RS may be nil.
* io.c (rb_io_getc): should process character based on external
encoding, when transcoding required.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@14619 b2dd03c8-39d4-4d8f-98ff-823fe69b080e