CustomFunctions.evaluate clones too much

[a701440]

Is it possible to avoid cloning a lot of AST in the CustomFunctions.evaluate. It appears that even for simple functions that don't use most of the arguments a lot of inefficient cloning is taking place. Perhaps this could be a configuration option. This way authors of custom functions could clone internally if needed when this option is set to false. Actually it's not clear why cloning is needed. Standard function packages don't seem to clone.