Deprecate Statistics::Descriptive2 and change any dependencies on it to Biodiverse::Statistics

[GoogleCodeExporter]

Statistics::Descriptive2 was written as Statistics::Descriptive seemed not to 
be maintained anymore.  This has changed in the last 12 or so months.  S::D2 
was also never released via cpan.

The only method difference between S::D2 and S::D is kurtosis, skewness and the 
percentile calculation.  Kurtosis and skewness have been submitted as patches 
for S::D, while the latter can be handled within a Biodiverse::Statistics 
module (as can kurt and skew until the patch is applied, assuming it is).

Original issue reported on code.google.com by shawnlaffan on 12 Jun 2010 at 9:07