Restoring the accidentally reverted r899802.


git-svn-id: https://plugins.svn.wordpress.org/akismet/trunk@942464 b8457f37-d9ea-0310-8a92-e5e31aec5664
Bump minimum WP version to 3.1; this should have been done in version 3.0.0.


git-svn-id: https://plugins.svn.wordpress.org/akismet/trunk@942467 b8457f37-d9ea-0310-8a92-e5e31aec5664