Reenable ..._SHLIBDEPS for .deb package

Without it, the .deb has no dependencies at all; the dependencies on
libc6 and libgcc1 aren't that important, but when built with
clang++-libc++, not listing the added libc++1 dependency is a bigger
deal.
Random: provide N(0,1) object

normal_distribution, in particular, benefits from being stored and
reused (rather than having new objects as needed) because it generates
values in pairs on every second call; not storing the object wastes
half the random draws.

This commit adds public Random::rstdnorm() to return a N(0,1), and
Random::stdnorm access to directly invoke the underlying
std::normal_distribution<double>.