python - typ: Add proper support for intervals.

Log Message:
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Add proper support for intervals.

However, in stdio, Python's datetime.timedelta does not support "months", so
just multiply the given months by 30 to get the days for the timedelta. This
appears to be what extract(epoch from <interval>) does when months are involved.

Modified Files:
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    typ/src:
        oidmaps.py (r1.2 -> r1.3)
        (http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/typ/src/oidmaps.py.diff?r1=1.2&r2=1.3)
        pstruct.py (r1.3 -> r1.4)
        (http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/typ/src/pstruct.py.diff?r1=1.3&r2=1.4)
        stdio.py (r1.1 -> r1.2)
        (http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/typ/src/stdio.py.diff?r1=1.1&r2=1.2)
        test.py (r1.1 -> r1.2)
        (http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/python/typ/src/test.py.diff?r1=1.1&r2=1.2)