python - ip: Implement some common code in Connector and Fitting

Log Message:
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Implement some common code in Connector and Fitting classes.

These were more abstract, but some common functionality could be implemented
here, so do so. In particular, the way in which Connectors are instantiated is a
bit difficult, so avoid the headaches of duplication by placing them here.

Also, introduce the idea of adaption for Interface classes. This provides the
ability to layer interfaces on already established connections, instead of
requiring a new Connector to be used.

Modified Files:
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    ip/src:
        abstract.py (r1.2 -> r1.3)
        (http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/ip/src/abstract.py.diff?r1=1.2&r2=1.3)

Added Files:
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    ip/test:
        abstract.py (r1.1)

(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/ip/test/abstract.py?rev=1.1&content-type=text/x-cvsweb-markup)