webrick/httputils: note Kernel#open behavior

I don't know who uses the load_mime_types method; but it is
conceivable that a user would want to read the results of a
command instead of reading a regular file to load MIME types.

None of the WEBrick-related code in Ruby or default/bundled gems
seems to rely on this method; but it is likely 3rd-party code does.

* lib/webrick/httputils.rb (load_mime_types): note Kernel#open behavior
  [Misc #14216]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@61402 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/webrick/httputils.rb

@@ -108,6 +108,8 @@ module WEBrick
     # Loads Apache-compatible mime.types in +file+.
 
     def load_mime_types(file)
+      # note: +file+ may be a "| command" for now; some people may
+      # rely on this, but currently we do not use this method by default.
       open(file){ |io|
         hash = Hash.new
         io.each{ |line|