inline tools::SvRefBaseRef typedef

..it is only used in two places

Change-Id: If333936b26592ed44d3525f2eb3c21aafde7dddc
inline SvCompatWeakHdlRef typedef

.. only used in 2 places in the same file

Change-Id: I5dc1dc77c3841bf86134f6a48597f8c1e71b2b3f
add some comments to include/tools/ref.hxx

Change-Id: Ic38d7f5f816f2a91bfb468c0b7fb241b084a0c44