Grob name change results in duplicated (and missing) geoms

[wch]

The change in 0719eed changed the rendering of some geoms.

See the visual tests comparing that commit to its parent:
http://stdout.org/~winston/vtest/diff/

It appears that a single geom is being drawn multiple times. For example, in the polar tests, there should be six "pie slices" but there is only one -- but the edge looks jagged, suggesting that it's there are multiple wedges with the exact same dimensions being plotted on top of each other. Also, some of the dotplot tests are semi-transparent, and they have become more opaque.

[wch]

I reverted 03a7962.