Lots of undefined behavior found by sanitizer

See e.g. this message about incorrectly casting an enum value that seemed pretty serious: https://list.coin-or.org/pipermail/cbc/2017-October/002261.html

To reproduce, compile Cbc with Clang and AddressSanitizer enabled and lots of crashes should show up. Some crashes are relatively easy to fix, but others are much trickier.