--rerun-incomplete flag not working

[matthewabirk]

I had to kill 9 elvers because I ran out of disk space. Now when I try to rerun, it suggests including the --rerun-incomplete flag. But when I add this, it complains that it does not recognize it.

[bluegenes]

--rerun-incomplete is a snakemake flag, and is not integrated into elvers. The python api equivalent seems to be force_incomplete. I've added this to #148, and it will be integrated into the main codebase with that branch.