Implement CASE on fixnums or characters by binary search

[Paul F. Dietz]

CASE forms in which the constants are fixnums or characters are currently implemented as linear searches. Instead, be smarter and exploit the ordering of these values to do binary search.

Example:

(defun f (x) (case x (#.(loop for i from 0 to 25 collect (code-char (+ i (char-code #\a)))) t)))

(defun g (x) (case x (#.(loop for i from 1 to 30 collect i) t)))

[Douglas Katzman (dougk)]

These examples both turn into jump tables (on supported architectures) now.

There's an argument to be made that the CASE macro could be smart enough to expand G into
  (if (typep x '(integer 1 30)) t) nil)
Patches are welcome, as always.