Allow formula to skip docs removal

Library/Homebrew/brew.h.rb

@@ -383,11 +383,11 @@ class Cleaner
     # you can read all of this stuff online nowadays, save the space
     # info pages are pants, everyone agrees apart from Richard Stallman
     # feel free to ask for build options though! http://bit.ly/Homebrew
-    (f.prefix+'share'+'doc').rmtree rescue nil
-    (f.prefix+'share'+'info').rmtree rescue nil
-    (f.prefix+'doc').rmtree rescue nil
-    (f.prefix+'docs').rmtree rescue nil
-    (f.prefix+'info').rmtree rescue nil
+    unlink = Proc.new{ |path| path.unlink unless f.skip_clean? path rescue nil }
+    %w[doc docs info].each do |fn|
+      unlink.call(f.share+fn)
+      unlink.call(f.prefix+fn)
+    end
   end
 
 private