libwebp environments updates

[Andrew Clark (arjclark)]

You may be aware of recent security vulnerabilities identified with the webp library. We have taken a look at ANTS environments and found it present at vulnerable versions being pulled in to ANTS 1.1 onwards. To address this we have issued ANTS 1.1.2 and updated the lock files present at head of trunk for those building their own developer environments. Please update at your convenience.

The update, as we've had to apply it, should not change results for patterns captured in our unittests and rose-stem testing.