Uniform handling of get and post handlers in RequestHandler

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This is a feature request:

When creating a web application for processing HTML form, one is often lead to 
process the form post data by the same RequestHandler that displays the form 
(i.e. to use the post-back idiom).

In RequestHandlers like these the get and the post method usually share common 
code to set up the context. It would be nice if the default dispatch method of 
RequestHandler would call a common method (for example like "update" on Zope 
views) once it has determined args and kwargs before it calls a handler like 
get and post with these args and kwargs.

Original issue reported on code.google.com by marc.nieper@gmail.com on 2 Nov 2011 at 7:15