* partly fix state_db getCode to get 20 new working GeneralStateTests; remove 2 functions which existed as workarounds; switch all remaining setBalance calls in GeneralStateTestRunner to subBalance (addBalance calls already changed)
* two of the 20 new tests don't work in 32-bit builds
* fix 32-bit issue in AppVeyor
* allow another dozen or so GeneralStateTest fixtures which work on 64-bit, but not on 32-bit platforms, to safely-fail, but demarcate them separately to facilitate debugging
* steal fa672600eb from @coffeepots fix-int32-high-zero branch