using cznic.1 release string for upstream packages ensures they are
prefered over downstream ones and that their versions don't collide
which was causing issues for users with both downstream and upstream
packaging repos enabled.

Following statements are true according to `dpkg --compare-versions`:

    1.2.3-1   < 1.2.3-cznic.1
    1.2.3-999 < 1.2.3-cznic.1

So upstream packages should always take precedence over downstream
packages of the same version.