[svn-r24161] Purpose: More on HDFFV-7520 and HDFFV-533

Description:
    - Completed the changes in revisions r22836 and r23438 with improvement
    on wrappers such as reference, dereference, get region, and set/getcomment.
    - Added more tests.
Platforms tested:
    Linux/32 2.6 (jam)
    SunOS 5.11 (emu)
    Linux/ppc64 (ostrich)

c++/src/H5Attribute.cpp

@@ -44,6 +44,7 @@ namespace H5 {
 #endif  // H5_NO_STD
 #endif
 
+class H5_DLLCPP H5Object;  // forward declaration for UserData4Aiterate
 //--------------------------------------------------------------------------
 // Function:	Attribute default constructor
 ///\brief	Default constructor: Creates a stub attribute