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/source.c

@@ -46,7 +46,7 @@
 #define ABSOLUTE_MAX_LATENCY (10*PA_USEC_PER_SEC)
 #define DEFAULT_FIXED_LATENCY (250*PA_USEC_PER_MSEC)
 
-static PA_DEFINE_CHECK_TYPE(pa_source, pa_msgobject);
+PA_DEFINE_PUBLIC_CLASS(pa_source, pa_msgobject);
 
 static void source_free(pa_object *o);