[svn-r11264] Purpose: Additional code improvement

Description:
    Used "using" declaration and directive better to reduce namespace
    pollution.

Platforms tested:
    Linux 2.4 (heping)
    SunOS 5.8 64-bit (sol)

c++/src/H5DataSet.cpp

@@ -35,6 +35,9 @@
 
 #ifndef H5_NO_NAMESPACE
 namespace H5 {
+#ifndef H5_NO_STD
+    using namespace std;
+#endif  // H5_NO_STD
 #endif
 
 //--------------------------------------------------------------------------