Disabling the generational collector

Something that fell out naturally from the recent GC refactoring is supporting -generations=1. This disables the generational GC entirely, reverting to the old-fashioned Cheney collector. This has exactly one valid use case: severely memory constrained environments. In such an environment, you'd build a minimal image (something that can be done now by editing core/bootstrap/boot-stage1.factor, but there are no nice tools for this ye), and the overhead of a non-generational collector wouldn't be too bad, since your heap will be small anyway.