Django version requirements

[meissls]

Currently the minimal required version of Django is 1.2 (see /doc/en/users/install.html). However the "on_delete" attribute introduced in r935 is only available with version >=1.3 (see  Django doc.

Thus either we relax the requirement on the Django version to >=1.3 or don't use the "on_delete" attribute.

Note that #99 would be resolved with switching to 1.3 too.

[martin.paces]

Required Django version has been increased from 1.2 to 1.3 in r1588 .