Added generic signal handling mechanism based on pipes to synchronize
signals with the main poll loop.

diff --git a/server/thread.h b/server/thread.h
index 21fcdcb..f30ef4c 100644
--- a/server/thread.h
+++ b/server/thread.h
@@ -126,7 +126,7 @@
 
 /* ptrace functions */
 
-extern void sigchld_handler();
+extern void sigchld_callback(void);
 extern int get_ptrace_pid( struct thread *thread );
 extern void detach_thread( struct thread *thread, int sig );
 extern int attach_process( struct process *process );