In f08119b01e, the default syntax for the script protocol's callback made it so the callbacks looked like `OpenLayers.Protocol.Script.registry[c1]`. This essentially breaks the script protocol everywhere except where `c1` is defined and equals "c1" (the string).
Tests with this change demonstrate that default callbacks will now look like `OpenLayers.Protocol.Script.registry['c1']` (properly accessing the `c1` property of the registry object).
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