Show attachments lacking a Content-Disposition: Bug #713830

Attachments without Content-Disposition are now generated and shown
in the client.  This requires a database upgrade as well as rescanning
all messages to generate the previously missing attachments.

In addition, this upgrade now stores the attachments' Content-ID in
the database.  This makes it much easier for the client to associate
a particular MIME section in the RFC822 message with an attachment in
the database and on disk.
Remove inline images that are included by Content-ID reference
Encode Content-ID before inserting into HTML

Also, watch for null when fetching node from the DOM.
Escape the CID when searching as well

Also, add a debug statement, since no match results in an null element,
not an error.