Comment 4 for bug 1099943

The extrude code requires updating in many regards including the 'chaining' that Jon highlights, that does not function properly on the sphere. It's also not good to have the majority of the code duplicated in Extrude.F90 and Extrude_radially.F90. I have a development branch to update the runtime 3d mesh generation which includes a fix to sigma layers and the merge of the extrude modules. It's not yet in the trunk and under testing, but so far looks to work robustly.