T tracer: don't depend on T_BUFFER_MAX anymore in the tracers

Whenever the value T_BUFFER_MAX changes, the tracers had to
be recompiled. The only reason why it was needed is because we
used some fixed size buffers to read events. This commit removes
this restriction.

Also, with the basic simulator, this value T_BUFFER_MAX now comes
with an #ifdef which would have required some special hackish-level
tricks in the tracers, which is not good.

Let's just allocate memory when needed.

common/utils/T/tracer/event.h

@@ -1,6 +1,7 @@
 #ifndef _EVENT_H_
 #define _EVENT_H_
 
+#include "utils.h"
 #include "../T_defs.h"
 #ifdef T_SEND_TIME
 #include <time.h>
@@ -37,7 +38,7 @@ typedef struct {
   int ecount;
 } event;
 
-event get_event(int s, char *v, void *d);
+event get_event(int s, OBUF *v, void *d);
 
 #ifdef T_SEND_TIME
 event new_event(struct timespec sending_time, int type,