isEq(DQuaternion q, double epsilon) is const

[tzaeschke]

public boolean isEq(DQuaternion q, double epsilon) {
        return Math.abs(this.w - q.w) <= epsilon && Math.abs(this.x - q.x) <= epsilon && Math.abs(this.y - q.y) <= epsilon && Math.abs(this.z - q.z) <= epsilon;
}

The method should take DQuaternionC as argument.