dN/deta tasks no longer make symmetric extensions, nor

dN/deta tasks no longer make symmetric extensions, nor
rebinned histograms.  This is after all better done in the
drawing macros.

dN/deta tasks can now use an AliAnalysisUtils object to
filter pile-up events.   Also, flags are set in the AOD
object to distinguish the kinds of pile-up (SPD,Track,Out-of-Bunch)

dN/deta tasks can also filter on SPD outlier events - i.e.,
events where the number of clusters in both SPD layers
exceeds some number proportional to the number of tracklets.

Further more, the dN/deta tasks has undergone some clean-up,
in particular we only write mergeable objects in the analysis
phase.