First part of Exchange meeting request/reply implementation

* Added two columns to Attachment in EmailProvider
  content: content that is written directly as an attachment
  suppressDisposition: to suppress the content-disposition header
  All meeting invitation emails use these two columns; the first
  for ics attachment data (which is quite small, rarely over 1k),
  and the second to indicate NOT sending the content-disposition
  header; without this, Exchange will consider the ics as an
  attachment rather than an iMIP style message (rfc2447)
* Modified tests to include these columns; added upgrade code for
  new database version
* New columns and code are designed to be usable outside Exchange,
  although there are no other clients of the code at this point.
* Modified Rfc822Output to use the content field, if present, in
  lieu of retrieving attachment data via URL; added support for
  suppressing the Content-Disposition header
1 file changed