Compute all the details needed to create our 25bp rerun given just

Compute all the details needed to create our 25bp rerun given just
a runfolder.
(This assumes more than the --gerald/-o version that I first
implemented, which is still available).

Now you can give rerun_eland a runfolder name, and it will (if there's
only 1 run found by pipeline.runfolder) extract the bases from that
into a new Data/C1-<length+1> directory and should launch eland.