modify Balloc's [alloc_gen] and [free_gen] to support both [list2mem] and [list2nmem]
modify Balloc's [alloc_gen] and [free_gen] to support both [list2mem] and [list2nmem]

[BALLOC.rep_gen] now has two predicate arguments: one that is useful
for [list2mem] memories, and one that is useful for [list2nmem] memories.

mit-pdos/fscq-impl,mit-pdos/fscq-impl,mit-pdos/fscq-impl,mit-pdos/fscq-impl,mit-pdos/fscq-impl