Add Shaded Polygon to LineProfile Plugin Output

This addresses #865.  The output now contains a gray polygon with the same shape as the overlay region shown by the tool.  I also caught a bug when the line endpoints were floats (`draw.line` did not like them), so I converted the points to integers.  I tested this with all four line orientations.  I added a unit test for viewer/plugins/lineprofiler that uses mono and rgb images, as well as a thick line.  I am using a 32 bit install of Anaconda 2.7 on Ubuntu 12.04.

![screenshot from 2014-02-04 21 58 56](https://f.cloud.github.com/assets/2096628/2084201/1e780d24-8e1a-11e3-9fe0-caa0e6842db0.png)

![screenshot from 2014-02-04 21 59 02](https://f.cloud.github.com/assets/2096628/2084202/2192cbca-8e1a-11e3-993b-724ad82e9dda.png)

![screenshot from 2014-02-04 21 59 10](https://f.cloud.github.com/assets/2096628/2084203/25269712-8e1a-11e3-937f-0a1ba280fac3.png)