Only create VS6 bugfix routine if we are running VS6 and actually use it, this is to prevent an annoying warning about unused code

git-svn-id: https://agg.svn.sourceforge.net/svnroot/agg@81 ab9de31f-a152-4fe9-8809-95f286f9ca89
Add agg_renderer_base::fill(color&) method for blending a color. Complements the clear(color&) method, which copies the color.

git-svn-id: https://agg.svn.sourceforge.net/svnroot/agg@82 ab9de31f-a152-4fe9-8809-95f286f9ca89