Also move the declarations of `incore` and `core_alloc` to "memory.h".
Also correct SYMDEBUG to SYMDBUG. (I don't know if SYMDBUG works
because our build system never defines it.)
ind_t becomes an alias of size_t. ind_t becomes unsigned, so I edit
some code that was using negative ind_t. Some casts disappear, like
(long)sizeof(...) because the size is already a size_t. There are
changes to overflow checks. Callers with a size too big for size_t
must check it before calling the memory allocator. An overflow check
of BASE + incr in memory.c sbreak() now happens on all platforms, not
only when a pointer is smaller than a long.
My build shows no changes in share/ack/examples (except hilo_bas.*
changing with every build).
