1.0.30.51: fix for COERCE compilation regression

1.0.30.51: fix for COERCE compilation regression

Code of the form
  (defun foo (x)
    (declare (type simple-vector x))
    (coerce x '(vector (unsigned-byte 8))))
should not cause a full WARNING, but with the new COERCE transforms,
expanded into one of those IFs where one branch is dead, but the
compiler couldn't prove it.

Define a whole heap of new backend type predicates for all specialized
vectors, generalizing VECTOR-T-P.  (Some specialized vectors are
implemented using widetags, and so are excluded from these new
definitions).