[Research] internal representation of datsets

[Jeff Schneider]

Hi guys,

I just (quite painfully) discovered that our datset implementation actually 
stores doubles as floats internally in the something called a pvector.

I'd like to change these to be doubles so what I experienced doesn't happen to 
anyone else.  HOWEVER, that seems like a big change to the very core of the 
code.  And at the least it will certainly cause datsets to consume more memory 
internally.

Any thoughts/advice on doing this?  Or suggestions on alternate ways to not get 
burned by this again in those cases where you really want double precision?

Jeff.