fix uninitialized value warnings
Untaint abs_path of tempdir

After creating tempdir, gets the abs_path (which resolves
symlinks and updirs).  This protects from someone using
DIR with an absolute path containing symlinks, so is
safer than File::Spec->rel2abs because it also cleans up
absolute paths.

At that point, we know we had permission to create the
directory, so asking the OS for it's name is no more
risky.

This change makes all tests now pass under -T