Remove using std::XXX from headers

This is a bad practice to have using in headers because it pollutes the
namespace of any user of that header.
diff --git a/xmlserializer/XmlFileDocSink.cpp b/xmlserializer/XmlFileDocSink.cpp
index e3360ea..f73860c 100644
--- a/xmlserializer/XmlFileDocSink.cpp
+++ b/xmlserializer/XmlFileDocSink.cpp
@@ -33,7 +33,7 @@
 
 #define base CXmlDocSink
 
-CXmlFileDocSink::CXmlFileDocSink(const string& strXmlInstanceFile):
+CXmlFileDocSink::CXmlFileDocSink(const std::string& strXmlInstanceFile):
      _strXmlInstanceFile(strXmlInstanceFile)
 {
 }