Make t/iod-02filehandles.t clean up after itself

The iod-02filehandles.t test can leave a named pipe lying around in a
fixed location after the test completes. If your operating environment
involves multiple users and installations of Perl, then this can block
installation by anyone but the first installer.

Which isn't good.

So, fix the test to use `File::Temp::tempdir( CLEANUP => 1 )` and
everything is peachy.