ostruct.rb: match Symbol itself

* lib/ostruct.rb (method_missing): get rid of creating temporary
  string object for method name, match Symbol itself.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@50308 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/ostruct.rb

@@ -174,9 +174,8 @@ class OpenStruct
   protected :new_ostruct_member
 
   def method_missing(mid, *args) # :nodoc:
-    mname = mid.id2name
     len = args.length
-    if mname.chomp!('=')
+    if mname = mid[/.*(?==\z)/m]
       if len != 1
         raise ArgumentError, "wrong number of arguments (#{len} for 1)", caller(1)
       end