Properly report memory fault location.

Don't use %x, it gets cut off on x86-64, use %p instead.
Fix unreachable code warning due to 83e5661ae59addac315e6754013b3887b477570f

The second argument to ENSURE in ENSURE-NON-STANDARD-CLASS became
effectively non-optional, and the suppliedp check was leftover debris.
Fix some C compiler warnings.

Somewhere around 137ba2db2d362f03754ccd080ddbe96f7e3c5dc7 or thereabouts,
there was no need for so many nearly-the-same in-GC allocator routines.
Lower the limit of bytes in allocate-vector.

All the allocation routines in gencgc.c expect signed words, lower the
limit by 1 bit. The size is also double word aligned, which is done
with addition and masking, make sure that the addition doesn't
overflow.
x86-64 ALLOCATION, avoid overflows.

Use an unsigned comparison against the end of allocation, otherwise it
may overflow.