When using the variety of ShaderGroupBegin that takes a serialized
description of the group, errors in the individual 'shader', 'param',
or 'connect' commands were not bubbled up into a proper error message
for the ShaderGroupBegin call itself, nor caused it to return null
as the group.
Be more diligent about printing the group name with all group setup
errors. This includes in testshade, no longer accidentally clearing the
group name.
Larry Gritz
9d867289f7