add 'compose' to scheme/base; switch Help Desk to a mzscheme app

svn: r7979

original commit: bd7ced966ed54fedd5608a68ef8ec212a913e30d

collects/help/help.ss

@@ -1,7 +1,7 @@
 #lang scheme/base
 
 (require "search.ss"
-         browser/external
+         net/sendurl ; browser/external
          setup/dirs
          mzlib/cmdline)
 

collects/help/search.ss

@@ -7,7 +7,7 @@
          scribble/basic
          scribble/manual
          (prefix-in scheme: scribble/scheme)
-         browser/external
+         net/sendurl ; browser/external
          mzlib/contract)
 
 (provide/contract
@@ -84,8 +84,6 @@
       (send-url (format "file://~a" (path->string file)))
       (void))))
 
-(define ((compose f g) x) (f (g x)))
-
 ;; has-match : (listof regexp) -> entry -> boolean
 (define ((has-match search-regexps) entry)
   (ormap (λ (str)