File::Copy in Perl 5.10 does not copy permissions, so let's fix it
there and check for it elsewhere.
This reverts the two commits 06b3faa1bf
and 68c20b4e4e which did not help to fix
this issue as the initially suspected noexec mount wasn't really
there. Hopefully this finally resolves the test failures with Perl
5.10 in the new t/hook-apt.t.
If the security repo will be enabled or not currently depends on the
host's sources.list. So the resulting files differ depending on the
host where the test is run. Add a TODO item to break with that
"feature".
Also mention in the TODO list that a repo on archive.debian.org should
be used instead security.debian.org if the release is EoL. Currently
the security mirror is hardcoded into the hook.