agg changes again...

[thomas bonfort]

I got things working quite well removing them too...

1) fix the call to msImageInitAGG to not fall abck to msImageInitAGG
2) wrap the raster/wms layer drawing calls with AGG2GD before and GD2AGG after
3) one call to AGG2GD at the end of msdrawmap
4) modify msImageCopyMergeNoAlpha (actually create a msImageCopyMergeAGG)
5) a few changes for the legend/scale/reference drawing


I'd push this to after 5.0 however