Suggestion: make a long list faster

[ABG]

Watch this test of the Blockly preview:

Technical Preview: Blockly v10 Update

[Taunting your pet with food] This is a bug I call Taunting the Open Sockets. (Or Three Socket Monte) After a session of waving value blocks near the mouths of Make a List blocks and finally yanking a value out of one of its mouths, the blue mutator of the Make a List block stopped responding.