Restore interrupted delta computation

[GoogleCodeExporter]

When computation was interrupted e.g. by rebooting the computer, new attempt 
can start from the beginning of the last running pass.

Original issue reported on code.google.com by mantl...@gmail.com on 14 Sep 2012 at 6:37

[GoogleCodeExporter]

This issue was updated by revision 65a357c512eb.

When a pass is finished, temporary status file is created based on name of the 
delta file. When computation with the same delta is run again, computation 
starts from broken pass. It is user's responsibility to run the program with 
the same options. Mixing options between passes can lead to unexpected results.

Additional verify run when a broken run is finished is highly recommended.

Original comment by mantl...@gmail.com on 14 Sep 2012 at 6:41