Allow use of 1.0 in port shape definition.
Allow use of 1.0 in port shape definition.

Before, 1.0 was seen as an absolute value which made relative [0,1] x [0,1] defintions use None as 1.0.  We just don't allow a +1 for absolute differences now which shouldn't be a big problem.

vistrails/gui/pipeline_view.py:
  - QGraphicsPortPolygonItem.__init__: allow 1.0 as relative point placement

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