AGG could use vertex simplification at the pixel level

[tbonfort]

from the discussion thread in ms-dev found here:  http://www.nabble.com/vertex-simplification-tf4702867.html

for complex shapes rendered at large scales (i.e. very zoomed out), many vertexes of a shape may fall into the same pixel in image space.

this bug tracks the implementation of a relatively naive vertex simplification algorithm, that locally discards vertexes on a shape if they fall too close to their predecessor.

[tbonfort]

initial implementation in r7001