based on ruby_frame->iter altered by PUSH_ITER().

* eval.c (rb_thread_fd_close): should save current context before
  raising exception.

* io.c (set_stdin): preserve original stdin.

* io.c (set_outfile): preserve original stdout/stderr.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@1219 b2dd03c8-39d4-4d8f-98ff-823fe69b080e