[FIX] forums: Several fixes and improvements for process_inbound_mail for forums (was quite broken).
Use the html part if there's no text part available, and use the root 'body' section as a last resort (it's usually the source)
Ignore error report emails (needs more testing and possibly logging)
Try and find the message referred to in in-reply-to and use that topic if there is one
Also some code tidying and comments added

git-svn-id: file:///var/local/code.tiki.org/tikisvn/branches/13.x@52693 b456876b-0849-0410-b77d-98878d47e9d5
[FIX] forums: Restore mail in operation for feature_wiki_discuss.
Had been totally commented out as there was no feature or page_exists check - added them.

git-svn-id: file:///var/local/code.tiki.org/tikisvn/branches/13.x@52694 b456876b-0849-0410-b77d-98878d47e9d5
[FIX] ratings: Prevent notices caused when unserialising a non-array

git-svn-id: file:///var/local/code.tiki.org/tikisvn/branches/13.x@52695 b456876b-0849-0410-b77d-98878d47e9d5