view3d: convertVTPtoOBJ: Close output file to ensure it gets flushed immediately.
mesh extraction: Join the extraction thread before closing the window.
DataExportOptionsDlg: Don't auto-set a new axis order when the dialog is initialized.
Closes #880.  Doesn't take care of #701, but at least the behavior is consistent whether or not the user did/did not open the export options dlg.