Bump 2.2.x branch docs to refer to itself as 2.2.

(The code does not refer to itself as 2.2 yet; but the docs need to do so to
ease the release process.)


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@332906 13f79535-47bb-0310-9956-ffa450edef68