Optimize MAKE-ARRAY on unknown element-type.

Reimplement %vector-widetag-and-n-bits without using subtypep,
providing an order of magnitude speed up.

Out of line make-array :element-type 'character also caused to cons
twice larger than needed vectors on x86-64.
(Though that wasted space was reclaimed after GC).

Closes lp#1004501.