* NodeBuilder work: specifically, convenience builders. "a && b && c || d && e"

* NodeBuilder work: specifically, convenience builders.  "a && b && c || d && e"
  (etc.) now work for Nodes a, b, c, d, e.  Also refcounting fixes for
  NodeBuilder in certain cases

* (various places) don't overload __gnu_cxx::hash<>, instead provide
  an explicit hash function to hash_maps and hash_sets.

* add a new kind of assert, DtorAssert(), which doesn't throw
  exceptions (right now it operates like a usual C assert()).  For use
  in destructors.

* don't import NodeValue into CVC4 namespace (leave under CVC4::expr::).

* fix some Make rule dependencies

* reformat node.h as per code formatting policy

* added Theory and NodeBuilder unit tests