hdf5_ep

[svn-r4979] Purpose:
    Adding support for dll
Description:
    Added the definition of __DLLCPP__ depending on:
        HDF5_CPPDLL_EXPORTS: C++ API is to be exported - this name is
                generated by MSVC++ when the project was created.
        HDF5CPP_USEDLL: C++ API dll is to be used (imported.)  Any
                applications, that use the C++ API dll, must define this
                name in the project setting.
    On non-windows platforms, __DLLCPP__ is nil.
Platforms tested:
    Linux 6.2 (eirene)
    Windows 2000