Shellshock mitigation with BIG-IP iRules

@kollenh - After more feedback and recent findings on the vulnerability, I've modified the pattern to look for the exact string of characters "() {" within a header. We believe there are no standard cases where this would match outside of a custom application. I've tested against all known user agents for the major browsers with a zero false-positive match. Could you try it out with the latest, more restrictive, pattern? If you are still getting matches, you might want to attempt the first iRule and log out exactly which header was causing triggering the block.