Cleaner: add (commented-out) debugging information for permission changes

The cleaning step changes permissions on files. Added a commented-out block
that will show permission changes when doing verbose builds.

Since this output is not generally useful for even normal verbose builds,
added as commented-out code (I'm sorry) so that maintainers can uncomment
it when this functionality is needed for debugging.

Library/Homebrew/cleaner.rb

@@ -46,6 +46,13 @@ class Cleaner
     else
       0444
     end
+    # Uncomment this block to show permission changes using brew install -v
+    # if ARGV.verbose?
+    #   old_perms = path.stat.mode
+    #   if perms != old_perms
+    #     puts "Fixing #{path} permissions from #{old_perms.to_s(8)} to #{perms.to_s(8)}"
+    #   end
+    # end
     path.chmod perms
   end