Gives the advantage of only having to change the urls.py instead
of every link that has been set somewhere. This also verifies that
all parameters needed by the URL are given.
Mostly for testing purposes, but also to unify the usage of
buyable in templates.
This also fixes the problem of having to make the retrieved lists
for usersLast* unique manually.
Konrad Mohrfeldt
Sebastian Lohff
MasterofJOKers