NEWS updates.

  * Forgot to add a NEWS update to my recent commit involving the
internal-error logic.

  * And clarify that only vectors of boxed items may be stack-
allocated on PPC.
code/room: Improve type-format database initialization for simple vector types.

  * There has been a longstanding FIXME comment on a piece of code
which contains a hand-maintained list of specialized vector types
and the shift count for converting the length from elements to
octets.

  * It turns out that all of this information, plus the type names
that we currently do a song-and-dance with INTERN, SUBSEQ, and
MISMATCH to obtain, plus information for the string types, is
available from *SPECIALIZED-ARRAY-ELEMENT-TYPE-PROPERTIES*.  And
*S-A-E-T-P* is guaranteed to be up-to-date, as it's too central to
our implementation of UPGRADED-ARRAY-ELEMENT-TYPE and MAKE-ARRAY
for it to be allowed to break.

  * So, replace nasty KLUDGE of an initialization for simple
vector types with something more principled, making it explicit
which properties need to be derived and which are simply already
available, and picking off the one specialized array type that
needs to be handled differently (SIMPLE-ARRAY-NIL).
code/room: Completely rewrite MAP-ALLOCATED-OBJECTS.

  * The old version of M-A-O consisted of bizaare toplevel logic,
a scheme for figuring out what each heap object was and its size
that did not parallel what the garbage collector used and may or
may not have been correct, and relied heavily on inlining to
reduce consing.

  * This new version of M-A-O uses straightforward toplevel logic,
a scheme for figuring out what each heap object is and its size
that directly parallels what the garbage collector uses and is
verifiably correct, and relies heavily on the aligned unboxed
pointer to fixnum equivalence to reduce consing.

  * The new interface to M-A-O no longer includes the optional
"careful" argument, as it gains us nothing once the underlying
mechanism is so obviously correct.  sb-introspect has been updated
appropriately.

  * The way the new implementation walks the heap and page table
requires direct access to a "static" global variable in gencgc.c,
so the "static" attribute has been removed.

  * This implementation has been lightly tested on an x86-64 and
PPC, and it seems to work quite well, but there are still some
fairly obvious non-optimalities in terms of generated code (as
seen in the trace-file output from the cross compiler).  It does
pass the two test cases that exhausted the heap on PPC with the
previous implementation.