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/core.c

@@ -47,7 +47,7 @@
 
 #include "core.h"
 
-static PA_DEFINE_CHECK_TYPE(pa_core, pa_msgobject);
+PA_DEFINE_PUBLIC_CLASS(pa_core, pa_msgobject);
 
 static int core_process_msg(pa_msgobject *o, int code, void *userdata, int64_t offset, pa_memchunk *chunk) {
     pa_core *c = PA_CORE(o);