Fix an error when using pipes and PGRP_PIPE is enabled.
( exec 3>&1; : `echo >&3` )
bash: 3: Bad file descriptor

http://bugs.gentoo.org/92349

Patch from upstream

*** a/jobs.c
--- b/jobs.c
***************
*** 3456,3459 ****
--- 3901,3907 ----
    stop_making_children ();
    start_pipeline ();
+ #if defined (PGRP_PIPE)
+   pipe_close (pgrp_pipe);
+ #endif
    delete_all_jobs (0);
    set_job_control (0);