More conservative defaults in GENCGC
* Set GENCGC-ALLOC-GRANULARITY to 0, and thus fully disable the minimal
allocation size logic by default.
* Explicitly zero out pages that fall outside GENCGC-RELEASE-GRANULARITY,
instead of leaving them dirty, when releasing address space.
* Set large_object_size to 4 * MAX(PAGE_SIZE, GENCGC_ALLOC_GRANULARITY,
* I'm getting very strange failures in some branches that I can't replicate
on master, but let's be extra careful for now.