GDAL can't be used to read results for WMS layers

[warmerdam]

It seems that in Mapserver 3.5 and MapServer 3.6 it is not possible to use
GDAL to ingest the png or gif results of remote mapserver for a WMS layer
if no resampling is to occur. 

That is because the GDAL raster layer drawing code does not understand how
to handle layers with layer->transform set to MS_FALSE.  Also, the adfGeoTransform
within msDrawRasterLayer{GD} would be uninitialized in if there was no georef
info as is the case for a bare png or gif file without even a .wld file.  This
also can cause severe problems. 

The bug is now fixed in CVS (well the change will be committed very shortly)
but that is post MapServer 3.6. 

The workaround is to ensure that GD gif and/or png support is compiled in as
that will be used in preference to GDAL for non-transformed layers.

[fwarmerdam]

As noted, it is now fixed in CVS.  This report just for information.