(swallow, rb_io_each_byte, rb_io_getc): revert previous change.

* io.c (rb_io_eof, io_fread, appendline, swallow, rb_io_each_byte)
  (rb_io_getc, rb_getc): call clearerr before getc to avoid
  stdio incompatibility.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_8@8436 b2dd03c8-39d4-4d8f-98ff-823fe69b080e