Squashed 'extensions/AccountCaptcha/' changes from eddd4bc..8fd21ab

8fd21ab Stability improvements
20dafb3 Revert "Dummy rand()"
17c8253 Dummy rand()

git-subtree-dir: extensions/AccountCaptcha
git-subtree-split: 8fd21ab06f810c26a3c49e4e642771cbae740243
Update AccountCaptcha

Merge commit '4c1be8dfa68c97eab0a46ceb0b27235093bc6408'