[FIX] positionOfSubCollection-fix-avi ( [cd][er][su][et][sm] Recommend including in 3.9a )

[tomkoenig at mindspring.com]

Tested with 3.9a #6520.  Bug exists before cs and doesn't afterwards. 
Avi fix changes only two methods.
I'm attaching a second changeset with updated sunit TestCases for
ReadWrite and SocketStream.  The RWS test pretty much just adds the test
suggested by Avi.  The SS adds a basic test for the modified method and
comments out a couple of failing tests that were failing and pointless. 
Added class comments for both TestCases.
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