Fix for proper C++ conformance

[Wiz Aus]

Managed to get all the lilypond code to at least *compile* now, although a 
long way off linking and running!

The main changes I had to make is to add

 friend void _##NAME##_start_translation_timestep(NAME*); \
 friend void _##NAME##_stop_translation_timestep(NAME*); \
 friend void _##NAME##_process_music(NAME*); \
 friend void _##NAME##_process_acknowledge(NAME*);

to the end of #define TRANSLATOR_DECLARATIONS(NAME) in translator.hh

And then in translator.icc, I changed the differences of 
IMPLEMENT_FETCH_PRECOMPUTABLE_METHODS and
ADD_ACKNOWLEDGER, like so:

#define IMPLEMENT_FETCH_PRECOMPUTABLE_METHODS(T)                        \
 IMPLEMENT_PROXY_METHOD(T, start_translation_timestep)          \
 IMPLEMENT_PROXY_METHOD(T, stop_translation_timestep)                   \
 IMPLEMENT_PROXY_METHOD(T, process_music)                                       
        \
 IMPLEMENT_PROXY_METHOD(T, process_acknowledged)                                
\
 void                                                                   \
 T::fetch_precomputable_methods (Translator_void_method_ptr ptrs[])     \
 {                                                                      \
   ptrs[START_TRANSLATION_TIMESTEP] =                                   \
     ( & T::start_translation_timestep ==   \
       & Translator::start_translation_timestep) \
     ? 0                                                                \
     : (Translator_void_method_ptr) & _##T##_start_translation_timestep;    \
                                                                        \
   ptrs[STOP_TRANSLATION_TIMESTEP] =                                    \
     ( & T::stop_translation_timestep == & 
Translator::stop_translation_timestep) \
     ? 0                                                                \
     : (Translator_void_method_ptr) & _##T##_stop_translation_timestep;     \
                                                                        \
   ptrs[PROCESS_MUSIC] =                                                \
     ( & T::process_music == & Translator::process_music) \
     ? 0                                                                \
     : (Translator_void_method_ptr) & _##T##_process_music;         \
                                                                        \
   ptrs[PROCESS_ACKNOWLEDGED] =                                 \
     ( & T::process_acknowledged == & Translator::process_acknowledged) \
     ? 0                                                                \
     : (Translator_void_method_ptr) & _##T##_process_acknowledged;          \
 }


#define ADD_ACKNOWLEDGER(CLASS, NAME)                                           
\
 static void _##CLASS##_##NAME(CLASS * engr, Grob_info info)    \
 {                                                                              
                                        \
        engr->acknowledge_ ## NAME(info);                                       
     \
 }                                                                              
                                        \
 void CLASS ## NAME ## _ack_adder ()                                            
\
 {                                                                              
                                        \
   add_acknowledger 
((Engraver_void_function_engraver_grob_info)&_##CLASS##_##NAME, #NAME, 
&CLASS::acknowledge_static_array_); \
 }                                                                              
                                        \
 ADD_SCM_INIT_FUNC (CLASS ## NAME ## _ack_adder_initclass, CLASS ## NAME ## 
_ack_adder);


All this does is ensure that member functions aren't stored directly as 
standalone function pointers - it creates a thunk or proxy function to call 
the member function and then stores that.
The thunks get created whether they're needed or not, but maybe a really 
good compiler would optimization them out (doubtful).
I do have to ask though - why on earth not do these as regular virtual 
functions??

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