Neat 0.4.3: Fixing else for once

Minor bugfix: In a if x else b and a else b, b is now correctly refcounted if it is a
local variable.

State of play is still:

auto var = obj?.field? else return false;

if (auto var = obj?.field?) { }

The compiler has been ported to use this idiom internally: field.notNull has been replaced across
the board with the somewhat more ruthless, if accurate, field? else die (die being a thin wrapper around exit(1)). The relevant commit serves as a practical demonstration of breakelse in the guise of ?.

Note that ? is overloaded between error propagation and breakelse handling: it will return errors from
a sumtype, and it will treat nullable T as a sumtype of (T | null) and breakelse the null,
but not both at once. This occasionally necessitated the appropriately-irate fun()?? else die.