quared fits to histograms it is now also possible
to perform chi-squared fits to unbinned datasets containing a series of X and Y values
with associated errors on Y and optionally on X.

<p>These 'X-Y' chi-squared fits are interfaced through newly added method
<tt>RooAbsReal::chi2FitTo(const RooDataSet&,...)</tt>. By default the event weight is
interpreted as the 'Y' value, but an <tt>YVar()</tt> argument can designate any other
dataset column as Y value. If X errors are defined, one can choose to integrate