Messageid backup for subdomains, and more robust checking in general, and whitespace cleanup.

I had a few problems thati wanted to fix and they all got tied up. I hope it's OK to bundle these.

• I'm using the smtp module and gmail as the smtp server which seems to add it's on Message-ID: header regardless of what the mailcomment module has done. But the clients try to use the Message-ID from google, Mailhandler puts that in node->threading variable, and the backup ID never has a chance to get involved. So, I propose that we split out the check for the messageid validity and run it on its own AND if it fails, try using the backup messageid.
• My site uses a subdomain and the regex to parse out the backup messageID didn't work with subdomains. I updated it using a regex I found online, but this broke the fancy matching of the domain as a chunk so I switched to using strpos to find the domain. We should probably use stripos here, but I see that there's some concern about using stripos. I think it's OK to just move to using stripos and push a PHP5.x dependency on clients, but we can do that later.
• I found a handful of whitespace cleanups and other little code style things that I fixed along the way.