Model methods should accept decorators

[Adrian Holovaty]

Model methods don't accept decorators, and they should. Here's a snippet from imaurer on the django-developers mailing list:

The one thing I don't like is that I cannot add decorators like
classmethod. For instance, this method:

   @classmethod
   def clsmethod(cls):
       print "HERE in", cls

Blows up like this for me:

File "C:\www\django\core\meta\__init__.py", line 490, in __new__
   assert callable(v), "%r is an invalid model parameter." % k
AssertionError: 'clsmethod' is an invalid model parameter.

I am also not able to create a 'memoize' decorator for caching method
results in an instance. Instead, I either have to do the "if
_cache_blah: return _cache_blah" pattern in each method I want
cacheable or call out to a non-model function that can be memoized but
using a global LRU dictionary.

[Adrian Holovaty]

This is fixed in magic-removal.