* Minor code formatting stuff in src/expr/type.{h,cpp}. Concluded

* Minor code formatting stuff in src/expr/type.{h,cpp}.  Concluded
  Type code review and closed bug #25.

* Do assertions on Expr creation (public library interface) even when
  assertions are off.  Also a similar check for proper kind (in public
  interface) when Expr::getConst<>() is called.  This fixes a unit
  test that was failing in production builds (an exception wasn't
  thrown but should have been).

* kind::XOR must have exactly 2 arguments, not 2-or-more.