For scaling of the stat. errors on systematic variations always use
N_data from real data to get the scale factor - this prevents us from
having unrealistic errors just because the MC samples are larger.
This does not affect extraction from real data but is just a fix
for pseudo data extraction.
Remove global flag from script call
Make the calculated prediction errors not private but protected to allow
derived classes access to the vectors.
Introduce new member variable of extractor base class: m_requestPredictionErrors
handles requests for the prediction errors to be calculated. This currently happens
a) if the FLAG_NO_THEORYPREDICTION_ERRORS is not set. Then it will be included in the
   MC stat errors of every single extraction
b) if a child class requests the errors. This is currently done by
   extractorYieldPrediction
Only print warning if the flag was actually present - otherwise I
get confused...
Add new class extractorYieldPrediction deriving from extractorYield.
This class takes the calculated prediction errors (for either Q^2 or
Matching) and adds them to the MC data (not to the MC statistical error!)
Beautify some printout. Add an additional debug statement.