Not sure what I had been smoking when writing this class. It was
a total disaster with subsets. Fixed most, added some (but too few)
tests. :-(
Added a facility to add error details to the location
so that the user of bnd can find easy to process
details. Each message has an associated Location
object (Processor.getLocation(msg)). This location
now has a 'details' object. Example where used
is the Baseline, the Baseline.Info is now set
as the details for a baseline error.
Changed the algorithm to find the baseline for
baselining. This is a breaking change since 
I removed functionality. The old way had a boolean
that selected a fallback or not. I think this was
too confusing and should in general not affect 
anybody. However, need to talk to PK about the
consequences because I think he was responsible.

See #356