is important is that the WMS spec specifies that you should seperate layer
names with a ",", and we were encoding that, so compliant WMSes would attempt
to find a single layer with ","s in the name, instead of grabbing multiple
layers. The new way to specify multiple layers is to set:
layers: ['global_modis','landsat']
or the like.
Includes tests, signoff from SDE.
git-svn-id: http://svn.openlayers.org/trunk/openlayers@2232 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf
1d06490b2c