Fix two build problems with CSS

* `release` didn't minify CSS.
* `minifyCSS` didn't always incorporate the latest CSS source, since it operates in-place.
Merge pull request #962 from AnalyticalGraphicsInc/buildFixes

Fix two build problems with CSS
Fix modified polygon bounding sphere at a height above the ellipsoid.
Add unit test.
Fix bug where getMutuallyVisibleVertexIndex in PolygonPipeline could return an index of -1.
Merge pull request #964 from AnalyticalGraphicsInc/polygonBoundingSphere

Polygon bounding sphere
Merge pull request #966 from AnalyticalGraphicsInc/visibleVertex

Eliminate polygon holes