Alternate track assignment not handled when generating extract files

[dgesswein]

For some controllers the sector headers indicate that a track has been assigned an alternate. For formats that know how assignments are done the sparing information is printed but alternate track is not written to the correct location in the extract file. The information provided can be used to manually fix the file. Other controllers store that information in data tables stored on the disk. Handling those data tables is not planned.

[dgesswein]

Code added to handle when marked in header for formats that alternate track encoding is known.