The Yahoo API doesn't accept quotes in the callback (e.g. foo['bar']). Since the callback registry is an object and all identifiers are prefixed with "c" now, we can use dot notation.
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).
