Stop io/ftwtest deleting its own output.

Stop io/ftwtest deleting its own output.

If you rerun "make check" in a tree where some tests have already been
run, it will rerun io/ftwtest-sh because that test uses ftwtest.out,
the same name to which output is redirected, as its internal temporary
file, and then removes it on exit.

Clearly tests should not be removing the files to which their output
is redirected like that.  This patch changes the script to use a
different file as its internal temporary file, so the actual output
referenced in the makefile isn't removed.

Tested x86_64.

	* io/ftwtest-sh (testout): Change to $tmp/ftwtest-tmp.out.