RFR 8168979: @implNote for invalid FilePermission

[Wang Weijun]

Please take a review at

   http://cr.openjdk.java.net/~weijun/8168979/webrev.00/

This further clarifies what an invalid FilePermission behaves. A major behavior change is that <<ALL FILES>> now implies an invalid permission, I hope this is good to minimize incompatibility.

Thanks
Max