the end of the pipe to the parent. otherwise move->fdes and
the exec'd program and the exit handlers can interfere with file
descriptors still in use in parent ports.
* Makefile.in: Regenerated.
* popen.scm: applied fixes from Greg Harvey. use a guardian
and a gc-thunk so that cleanup is done if a pipe is garbage
collected or closed with close-port. use a weak hash-table instead of
an alist.
* boot-9.scm (reopen-file): deleted.
* popen.scm (open-output-pipe, open-input-pipe): moved from
boot-9.scm.
* popen.scm: new file.
