Added ConvertObjectToXml to avoid code duplication
The multi source control must split and recombine SourceControlData for sub source control blocks to work properly.
Added CanConvertXmlToObject to help migration code
The multi source control must cope with previous (buggy) information transparently
The conversion must be done once and for all and thus can be more precise.
Merge pull request #192 from obones/Issue196

Issue196