Fix brew cleanup: less pruning

Running `brew cleanup` (with no arguments or multiple arguments) will
run `brew prune` after _every_ cleaned formula, i.e. possibly after
every installed formula.

With this change it will instead only run `prune` after all formulae are
cleaned, and only when no arguments were given to `cleanup`.

Signed-off-by: Max Howell <max@methylblue.com>

Closes Homebrew#743

Library/Homebrew/brew.h.rb

@@ -262,8 +262,6 @@ def cleanup name
       puts
     end
   end
-
-  prune # seems like a good time to do some additional cleanup
 end
 
 def clean f

bin/brew

@@ -217,6 +217,7 @@ begin
           opoo "Formula not found for #{e.name}"
         end
       end
+      prune # seems like a good time to do some additional cleanup
     else
       ARGV.named.each { |name| cleanup name}
     end