Extended the profiling API. When using the variable stack trace depth

buffer format, the buffer can now also contain other events than just
stack traces. ATM these are only references to the image events
(created/deleted). Therefore we no longer have to flush the profiling
buffer after such an event, since the debugger can exactly match the
samples. Since we couldn't flush when the profiling timer hit while the
thread was in the kernel, that wasn't working that well anyway.
"profile -f" fails to translate stack trace addresses only very rarely,
now.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@27775 a95241bf-73f2-0310-859d-f6bbb57e9c96

headers/private/kernel/user_debugger.h

@@ -96,6 +96,9 @@ struct thread_debug_info {
 		int32			image_event;
 			// number of the image event when the first sample was written into
 			// the buffer
+		int32			last_image_event;
+			// number of the image event when the last sample was written into
+			// the buffer
 		bool			variable_stack_depth;
 			// record a variable number of samples per hit
 		bool			buffer_full;