This commit is a merge from the "betterstats" branch, which:

This commit is a merge from the "betterstats" branch, which:

* Makes Options an "omnipresent thread-local global" (like the notion
  of the "current NodeManager" was already).  Options::current() accesses
  this structure.
* Removes Options from constructors and data structures everywhere
  (this cleans up a lot of things).
* No longer uses StatisticsRegistry statically.  An instance of the
  registry is created and linked to a NodeManager.
* StatisticsRegistry::current() is similar to Options::current(), but
  the pointer is stowed in the NodeManager (rather than stored)
* The static functions of StatisticsRegistry have been left, for backward
  compatibility; they now use the "current" statistics registry.
* SmtEngine::getStatisticsRegistry() is a public accessor for the
  registry; this is needed by main() to reach in and get the registry,
  for flushing statistics at the end.