Add trailing slash to looked up link

[isnok]

Hi arthanson,

genericadmin.js creates the link to the object without a trailing slash, wich is fine as long as APPEND_SLASH is unset or True in settings.py. We do now have the case, that this is not enabled, and as a result the links to objects became unusable.

It's just a minimal fix, that is okay with our project and might help other people as well. But more generally I think genericadmin.js:108 does not handle the case correctly when getLookupUrlParams returns a nonempty string.