fix for multiprocessing naming convention

[YellowSub17]

When running dens, I got strange file names for my output files.

I have a feeling that the args_dict variable is persistent within a multiprocessing pool, so once _0 is completed, the _1 filename is created as `'6lyz_0'+'_1'. This continues to the end of the processing pool.

This change I propose here uses a '-' delimiter between denss jobs, splits the output grabs the first element which should be the run name.

This will fail if the run name has a '-' in it. Eg. The file 'my-cool-protein' will be truncated to 'my-0', 'my-1', etc., so there is probably a better fix then this.