illogical values for reference counter

[gernotstarke]

the ref-count is not logical:
e.g. having 3 references to a nonexisting file counts as 1 problem.

When fixing one of those 3, it still counts 1 problem, although 1 has already been fixed.

Locical solution: count every occurrence of
a recurring problem as ONE problem.

But: currently the nrOfFindings is counted by counting the nr of messages in SingleCheckResults.