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|_|S)a� The 'case' statements in a 'switch' come out of parsing with one
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        come out messy. This is a peculiarity of the C grammar. The following:

            switch (myvar) {
                case 10:
                    k = 10;
                    p = k + 1;
                    return 10;
                case 20:
                case 30:
                    return 20;
                default:
                    break;
            }

        Creates this tree (pseudo-dump):

            Switch
                ID: myvar
                Compound:
                    Case 10:
                        k = 10
                    p = k + 1
                    return 10
                    Case 20:
                        Case 30:
                            return 20
                    Default:
                        break

        The goal of this transform it to fix this mess, turning it into the
        following:

            Switch
                ID: myvar
                Compound:
                    Case 10:
                        k = 10
                        p = k + 1
                        return 10
                    Case 20:
                    Case 30:
                        return 20
                    Default:
                        break

        A fixed AST node is returned. The argument may be modified.
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