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DeferArgs supports asyncronous try/except/finally constructs

A new version of DeferArgs is available at the cheeseshop.

New in 0.2 are the attempt, catch, and cleanup decorators. These mirror the functionality of try, except, and finally. Any deferargs decorated function can be followed immediately by any number of error handlers decorated as @catch(ErrorType) or @catch() to catch all, with the same semantics as except clauses if they were after a try block that surrounded the code in the function. The catches can all be followed with a cleanup decorated function, which will be called when everything else is done, errors or not.

There is also a convinience decorator called attempt, which automatically calls the function once a @catch() decorated handler is defined (signifying that all error handlers for it are prepared). Of course, calling it only really creates the deferred that fires when its arguments are ready, so you dont have to expect it to run for real untl after the attemp/catch/cleanup is completely defined.

As always, comments are welcome!

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