Make io/ftwtest-sh remove temporary files on early exit.

Make io/ftwtest-sh remove temporary files on early exit.

The test io/ftwtest-sh creates a directory that at some points during
the test does not have execute permission.  To avoid leaving behind
such a directory that prevents the build directory from being removed
with a simple "rm -rf", it traps various signals to make the directory
executable and remove it before exit.  However, this doesn't cover the
case where one of the tests simply fails (which happens with cross
testing if testing on a remote system where the path to the build
directory involves a symlink, or if that remote system fell over
during testing - I think the latter is the case where the directory is
left behind with bad permissions).

This patch makes that test also trap signal 0 (exit) so that the
directory gets properly removed in such failure cases as well.

Tested in both configurations where the test passes and where it fails
to verify that the result of the test is unchanged but the directory
is no longer left behind where it was previously left behind.

	* io/ftwtest-sh: Also trap on exit to remove temporary files.