[ENH] Limit document sampling, allow engines to expose debug information

git-svn-id: file:///var/local/code.tiki.org/tikisvn/trunk@52552 b456876b-0849-0410-b77d-98878d47e9d5
[ENH] Exclude all of user's current favorites from recommendations

git-svn-id: file:///var/local/code.tiki.org/tikisvn/trunk@52553 b456876b-0849-0410-b77d-98878d47e9d5