Fixed last dialog of export assistant, which was blank
Merge branch 'fix_assistantexport'

The export assistant ended with a blank dialog box with Close button. The
code indicated it should end with a friendly message to the user telling
of the successful export. Removed some "manual" sequencing lines so as to
allow the sequencer to do its own proper thing. Final dialog box appears
correctly now. Also tweaked messages on a couple of the dialog boxes.
HT: Birch Champeon for pointing out the bug and giving assistance on fixing
it.