Fix two bugs related to pod files outside of pod/

Fix two bugs related to pod files outside of pod/

Commit 1721346e4e420217, which allowed buildtoc to handle files outside of
pod/, had two bugs when processing files from outside of pod/

Firstly, the call to podset() for the core pods needs to pass in the short
name of the pod, not the name with the path in it (ie $_->[4], not $_->[1]),
else the =head2 entry for that pod will have the pathname in it.

Secondly, buildtoc must take care to avoid outputting the contents for these
pods twice - once when read from cpan/ or dist/ using the path in pod.lst,
and once from the file as found in lib/