block: fix infinite loop in __getblk_slow
Add & enable frandom

Idea from loosethisskin
frandom kernel random number generator: http://www.billauer.co.il/frandom.html

Squashed commit of:
https://github.com/f1vefour/supernatural-kernel/commit/8564e1af9b62f0c946afd7eef8bcc12344137353
https://github.com/f1vefour/supernatural-kernel/commit/95c81553596a0368212936c71f7d2f470f5d4803
https://github.com/f1vefour/supernatural-kernel/commit/5c1ef4b7565b6bf1b8807a05f369ec9df2ef8dce