object: speed up type verification by not relying on strcmp()

Instead of using string contents for type identification use the address
of a constant string array. This should speed up type verifications a
little sind we only need to compare one machine word instead of a full
string. Also, this saves a few strings.

To make clear that types must be compared via address and not string
contents 'type_name' is now called 'type_id'.

This also simplifies the macros for declaring and defining public and
private subclasses.

src/pulsecore/sink-input.c

@@ -44,7 +44,7 @@
 #define MEMBLOCKQ_MAXLENGTH (32*1024*1024)
 #define CONVERT_BUFFER_LENGTH (PA_PAGE_SIZE)
 
-static PA_DEFINE_CHECK_TYPE(pa_sink_input, pa_msgobject);
+PA_DEFINE_PUBLIC_CLASS(pa_sink_input, pa_msgobject);
 
 static void sink_input_free(pa_object *o);
 static void set_real_ratio(pa_sink_input *i, const pa_cvolume *v);