minor single mode bug fixed

fdtx.tcl

@@ -727,7 +727,7 @@ proc fdt:apply { w dialog } {
 		    puts $log "set probtrack(y) $probtrack(y)"
 		    puts $log "set probtrack(z) $probtrack(z)"
 		    puts $log "set probtrack(units) $probtrack(units)"
-                    set flags "--mode=single --seedref=$probtrack(reference) -o $probtrack(output) -x ${filebase}_coordinates.txt $flags"
+                    set flags "--mode=simple --seedref=$probtrack(reference) -o $probtrack(output) -x ${filebase}_coordinates.txt $flags"
 	       } 
                seedmask {
 		     if { $probtrack(bcyn) } {