Add a simple function for checking for membership in the fieldListMap.

git-svn-id: svn://anonsvn.kde.org/home/kde/trunk/kdesupport/taglib@572680 283d02a7-25f6-0310-bc7c-ecb5cbfe19da

ogg/xiphcomment.h

@@ -156,6 +156,13 @@ namespace TagLib {
        */
       void removeField(const String &key, const String &value = String::null);
 
+      /*!
+       * Returns true if the field is contained within the comment.
+       *
+       * \note This is safer than checking for membership in the FieldListMap. 
+       */
+      bool contains(const String &key) const;
+
       /*!
        * Renders the comment to a ByteVector suitable for inserting into a file.
        */