[FIX] forum import: Revert r46727 and r49710 - avoid fatal errors by restoring comments lib and class used for list_forums function call; use proper variable for temp folder so that file to be imported can be found; handle null values causing server errors for some fields; improve parsing which was mangling forums posts; keep php line breaks from displaying in the imported forum posts. 
[SEC] forum import: parameterize database insert; change $_REQUEST to $_POST and filter

git-svn-id: file:///var/local/code.tiki.org/tikisvn/branches/12.x@50260 b456876b-0849-0410-b77d-98878d47e9d5