compilation-scroll-output should be an autoload

[Christopher S. Kush]

Context-diff patch to the 21.1 compile.el appears on next page.

-- 
   "One does not wait for (X)Emacs to load,
    one jumps up and down with excitement."
                   -- Henrik Enberg

***************
*** 690,695 ****
--- 690,696 ----
    (let ((null-device nil))            ; see grep
      (grep command-args)))
  
+ ;;;###autoload
  (defcustom compilation-scroll-output nil
    "*Non-nil to scroll the *compilation* buffer window as output appears.