Expose who's the base and who's the exponent
vectorized MultiPdf, nexted AddPdfs, RooExponential and RooPower
fix bug in recursive addpdf splitting (the default constructor of RooAbsReal doesn't seem to work)
MultiPDFs: no need of setDataDirty if unpacking them, but still need to remember them to get the penalty term
merged RooMultiPdf printValue
Merge pull request #81 from gpetruc/vectorizing_multipdf

Bugfix in recursive RooAddPdf splitting (needed for Hgg), and vectorizing multipdf (off by default)
Merged after validation on full H->gg card: 20 point scan of mu, deltaNLL values within 10^-5 from results in master (often much closer), time reduced by a factor 3 with ADDNLL_MULTINLL=1