F3 Quit File
--------------------------------------------------------------------------------

    Abandons any changes made in the file and closes or kicks the file
    out of the current window.  If you are editing multiple files or
    have multiple windows, TDE searches for any invisible files to
    display in the current window.  If no invisible windows are found,
    TDE combines windows.  If this is the only file being edited, F3
    quits TDE.  If you made any changes to the file, it asks you if
    you want to abandon them.  You can create an invisible window when
    you load in a file over the current file.  Nothing happens to the
    invisible file or window - you just can't see it.

    When I added vertical windows, this routine became a LOT more
    complicated.  To keep things reasonably sane, let's only close
    windows that have three common edges, eg.

                +-----------------+
                |      |    no    |
                |      |----------|
                |      |yes1 |yes1|
                |  no  |----------|
                |      |   yes2   |
                |      |----------|
                |      |   yes2   |
                +-----------------+

    Windows with 'no' cannot be closed.  Windows with 'yes' can be
    combined with windows that have the same yes number.