title: Schema with xsd:any - XmlReader validation error
body: <p>I have problem with types in my schema when trying to use xsd:any element
  During validation i've got validation exception: The 'MerchantAccount' element is not declared. </p>
  
  <p>The idea is to have ability to specify any properties and values within ExtendedProperties element.
  Please advice what am i doing wrong.</p>
  
  <p>Part of the schema</p>
  
  <pre><code>...
  &lt;xsd:complexType name="ExtendedPropertiesType"&gt;
      &lt;xsd:sequence&gt;
        &lt;xsd:any minOccurs="0" maxOccurs="unbounded" /&gt;
      &lt;/xsd:sequence&gt;
  &lt;/xsd:complexType&gt;
  
  &lt;xsd:complexType name="ProcessorInstanceType"&gt;
    &lt;xsd:all&gt;
      &lt;xsd:element name="Id" type="xsd:string" /&gt;
      &lt;xsd:element name="Descriptor" type="xsd:string" /&gt;
      &lt;xsd:element minOccurs="0" name="ExtendedProperties" type="ExtendedPropertiesType" /&gt;
    &lt;/xsd:all&gt;
    &lt;xsd:attribute name="name" type="xsd:string" /&gt;
  &lt;/xsd:complexType&gt;
  ...
  </code></pre>
  
  <p>Part of xml file:</p>
  
  <pre><code>...
  &lt;ProcessorInstance name="aaaa"&gt;
    &lt;Id&gt;37fc527b-2845-43d0-99ca-ac1ff6f0ed86&lt;/Id&gt;
    &lt;Descriptor&gt;Test&lt;/Descriptor&gt;
  
    &lt;ExtendedProperties&gt;
      &lt;MerchantAccount&gt;1111&lt;/MerchantAccount&gt;
    &lt;/ExtendedProperties&gt;
  &lt;/ProcessorInstance&gt;
  ...
  </code></pre>
  
  <p>Validation code:</p>
  
  <pre><code>private static XmlDocument loadConfigurationXml(FileInfo configFile)
      {
          //load schema
          var sr = new StringReader(Schemas.ConfigurationSchema);
          var schema = XmlSchema.Read(sr, (o, ea) =&gt; { throw ea.Exception; });
          //validate against the schema
          var schemas = new XmlSchemaSet();
          schemas.Add(schema);
          var readerSettings = new XmlReaderSettings
          {
              ValidationType = ValidationType.Schema, 
              ValidationFlags = XmlSchemaValidationFlags.ReportValidationWarnings,
              Schemas = schemas,
          };
          readerSettings.ValidationEventHandler += (o, ea)=&gt;
          {
              throw new PaynetValidationException(
                  string.Format("Invalid configuration file, see schema for details: {0}", 
                                ea.Message), 
                  ea.Exception);
          };
          var reader = XmlReader.Create(configFile.FullName, readerSettings);
          //parse and validate config file
          while (reader.Read()){}
  
          var ret = new XmlDocument();
          if (configFile.Length != 0)
              ret.Load(configFile.FullName);
  
          return ret;
      }
  </code></pre>