__repr__ overloaded for short_descriptions in admin interface

[aaronsw]

The admin interface abuses repr to get its short_descriptions for listing objects. Instead, it should have a new function (perhaps short_description or something like that) to generate these things. Then, perhaps by default, repr can be '<'+classname+': '+short_description+'>' which is much more appropriate for the REPL situations in which repr is traditionally used.

If you have to use a special function, perhaps it could be str.

[Tom Tobin <korpios@…>]

Duplicate of #710.