Fix naive introspection when using Django decorators

[Jeremy Dunck]

It's fairly well-known that decorators are useful, but raise some issues.

Example:

def decorate(f):
   def wrap(*args, **kwargs):
       print "called"
       return f(*args, **kwargs)
   return wrap

@decorate
def add_to(augend, addend):
   "Adds stuff"
   return augend + addend

Introspecting add_to, undecorated, would have a name of 'add_to'
and doc of 'Adds stuff'.

After decorating, add_to.name becomes 'wrap' and doc becomes None.

================

In Python 2.5+, there's functools.wraps, which takes care of the
problem of introspection on decorated functions by copying attributes
from the wrapped function.

​http://docs.python.org/lib/module-functools.html

Django already includes curry, which is roughly the same as
functools.partial, so it's pretty easy to implement functools.wraps.

The attached patch implements django.utils.functional.wraps, updates all Django decorators to use it, and includes tests to verify that the fixing-up works.

[Jeremy Dunck]

patch against 6454