For performance reasons.

Signed-off-by: Damien PIQUET <piqudam@gmail.com>

Nodes can have different apt sources, so changelog localtion can also differ.

Because 'apt-get dist-upgrade' also does not consider the package
selection state (as opposed to apt-get dselect-upgrade).

Because 'Update' only makes sense for users knowing apt-get
command line tool.

Work for some packages, but not for all security updates. Seems
Debian security team does not upload changelogs.

The previos approch did not detect new packages, like new kernels.

To make it compatible with 'apt-get changelog'