[IronPython] .NET attributes

[Charlie Moad]

> Take away decorator support and you'll lose at least this Python
> programmer...
> Decorators and attributes have at least some commonality, which is why
> this syntax ended up in Python in the first place...
> Allowing decorator syntax in places CPython doesn't is better than not
> allowing it where it does...

So it sounds like people want decorator syntax for attributes.  Would
it be sufficient to check for inheritance from System.Attribute to
distinguish the two?  Also attributes being classes and decorators
functions might help.  I agree it is better to allow the decorator
syntax in more places than cpython than the alternative.