(Maint) Tempfile paths on Mac contain '+' which must be escaped

Previously, the test was failing on Mac, because Tempfile returns a path
of the form /var/folders/9z/9zXImgchH8CZJh6SgiqS2U+++TM/-Tmp-/foo, and
performing a regex match with it. Since '+' is a regex metacharacter it
must be escaped.

Reviewed-by: Daniel Pittman <daniel@rimspace.net>