Set the global variable eval_exit.

  This is set if *both* --eval and --exit are specified on the
 command line.  Because this implies that our curses UI won't
 be visible - or at least not for long.
  If eval_exit is present then write output to stdout.

  This is helpful to allow:

        lumail --eval "daily();" --exit

  The output from msg() will now go to the invoking console, rather
 than being lost.
  Added new test/demo-program.

    ./dump-parts ~/Maildir/.steve.org.uk/cur/1178920480.000011.mbox:2,RS
    File: /home/skx/Maildir/.steve.org.uk/cur/1178920480.000011.mbox:2,RS
    1 text/plain
    2 image/gif
    3 image/jpeg
    4 image/jpeg

  This is iterating over the body of the named message, and showing
 the multipart contents.

  We're intending to write three(??) primitives which will be similar
 to :

* get_body_part( N ) - Returns the named part.
* get_body_parts() - Which returns a table similar to the output above.
* has_body_part( "text/plain" ) - Returns a boolean.

  Somehow we'll wire things up so that a function can return text
 for body display.

  This is part of 114.
  Fixed comment.
  Ignore the built binary util/dump-parts
  Added some stub facilities for working with MIME-bodies.

  We've added three new primitives:

    * has_body_part( "text/plain" ) -> bool.
    * get_body_parts() -> table.
    * count_body_parts() -> int

  These functions currently return empty results, as
 `CMessage::body_mime_parts()` is a NOP.  However once that
 is fleshed out the primitives will work.

  The missing primitive is `get_body_part(N)` which will
 return the content.  I'll handle that shortly.

  This updates #114.
  Update the handling of cached ::name()

  This was bogus, but is now correct.
  Rationalze the headers.
  Rationalise the header-files that are included.
  Added function to toggle long/short names for maildirs.
  Cleanup header-inclusions.
  Moved primitives into files.

  Moved primitives into files based on purpose.

  Still not complete, but part of #125
  Document location of primitives
  Moved folder-related code to src/bindings_folders.cc
  Moved the index-functions to a new file.