wxDL_XXX macros and dynamic loading cleanup:

wxDL_XXX macros and dynamic loading cleanup:

1. Clearly document the wxDL_XXX macros; including their implicit usage
   of m_ok member variable
2. Made sure they're used in the same way in all places they are used
   (sometimes they were passed an object, sometimes a pointer, breaking
   compilation: see patch 1791288)
3. Don't allocate wxDynamicLibrary objects on heap unnecessarily (which
   removes the need to delete -- or leak, as it was -- them afterwards)
4. Some naming convention fixes

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@48625 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775