remove reliance on nasty global variables 'detector' and 'processing'

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A proposed way to do this is to re-form the detector and processing lists as S4 
objects. Then simulation functions such as 'expose', 'read', 'correct' and so 
on should become methods for the classes of those objects.

Then you don't need to assume the presence of a global variable for a 
particular function to work - that function is simply a method of an object 
that has to exist.

There are other advantages to this idea, one being that the names 'detector' 
and 'processing' are no longer special. You can call your detector and image 
processing objects anything. This could be useful in, e.g., simulating an array 
of modules (detector01 to detector16 for example).

Original issue reported on code.google.com by dgwater...@gmail.com on 27 May 2011 at 2:50