Fixed signature rendering. The plugin was showing only one signature and was overriding other user's signatures.
* Added caching so user's signature is remembered (for the current request) and not retrieved all the time.

git-svn-id: https://plugins.svn.wordpress.org/orbisius-bbpress-signature/trunk@842787 b8457f37-d9ea-0310-8a92-e5e31aec5664