Fix duplicated columns for count()

When a same aggregate function was used more than once in a 'having'
clause, count() added that function more than once to 'select'.
Stop shipping world writeable files in our tarball

The chain of failures would go as follows: when we prepare the tarball
we briefly copy all generated POD to our root dir so that the
manifest/distdir_copy process can pick it up. Then before the distdir is
ready we run a cleanup using ExtUtils::Install::uninstall. However
everything in the ditdir is hardlinked to our root dir, including the
files we "uninstall". EU::I::uninstall has a weird dance deep in its
source[1] where it explicitly does chmod(0666) on the file it is about
to delete (why?!). Thus we end up with world-writables in our distdir,
since the hardlinked inode still retains the result of that last chmod.

Switch to a manual cleanup, and leave EU::I alone.

[1] https://metacpan.org/source/YVES/ExtUtils-Install-1.54/lib/ExtUtils/Install.pm#L274