Enable Prefetching

Modify the Framework to prefetch products that were declared
to be consumed before running a module. This includes both
performing delayed reads of data from the ROOT file and
performing unscheduled execution of producers. Add code
that enforces that consume declarations are only in the module
constructor.

Note the only change external to the Framework (in DQM) is to
move the consumes call from beginJob to the constructor in
one module.
Merge pull request #1035 from wddgit/prefetch

Multithreaded framework -- Enable Prefetching