Prevent rasterizer_cells_aa<Cell>::sort_cells() from accessing two elements past the end of the array of cell block pointers, C/C++ only permits accessing one element past the end of an array

git-svn-id: https://agg.svn.sourceforge.net/svnroot/agg@78 ab9de31f-a152-4fe9-8809-95f286f9ca89
Add const qualifier to multiply and divide operators for agg_trans_affine/perspective

git-svn-id: https://agg.svn.sourceforge.net/svnroot/agg@79 ab9de31f-a152-4fe9-8809-95f286f9ca89