Bug fixes

• #5946 Inconsistent reference_time between deform and transform motion blur
• #5947 AiSetAppString() not working
• #5953 Wrong stats after destroying shape nodes
• #5964 LPEs not working with raw drivers
• #5969 Avoid gcc -Wall warning about strict-aliasing in AtParamValue
• #5973 Curves with varying UVs rendering wrong
• #5977 Shadow matte shader missing transparency with passthrough shader