#27 ZSI: Better implementation of NamedParamBinding

[GaryD]

I have improved the implementation of
NamedParamBinding. Now, we store the _Caller class on a
class attribute on Binding.

Advantages:
* Don't repeat the code for __getattr__
* Easier to subclass Binding in multiple ways (eg. in
combination with patch #1187145, you could easily
create a Binding that accepted named parameters and
used a proxy).

Disadvantages:
* None I can think of

There are probably other ways to do this (eg. pass the
_Caller class in as an __init__ parameter), but this is
what occurred to me.

[GaryD]

Use Binding class attribute to hold _Caller class

[Joshua Boverhof]

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I don't see a compelling reason to accept this patch, so the default is to reject it.