3f52aadd8dRerouted the global alternate stack to the end (lowest address) of each process stack. This fixes potentially shared stacks and allows the garbage collector to traverse stack frames even if a process is currently handling user-defined signals on the alternate stack. However, the alternate stack is used for catching segmentation faults caused by stack overflows, which may now reuse the last part of the stack and therefore corrupt stack traces. This is an experimental patch and may need improvement.