merge revision(s) 43112,43114,43117,43118: [Backport #8980]

	* io.c (rb_io_close_read): keep fptr in write_io to be discarded, to
	  fix freed pointer access when it is in use by other threads, and get
	  rid of potential memory/fd leak.

	* io.c (rb_io_close_write): detach tied IO for writing before closing
	  to get rid of race condition.  [ruby-list:49598]

	* io.c (rb_io_close_read): duplex IO should wait its child process
	  even after close_read.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_0_0@43144 b2dd03c8-39d4-4d8f-98ff-823fe69b080e