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

diff --git a/server/ptrace.c b/server/ptrace.c
index 002bc8f..5323007 100644
--- a/server/ptrace.c
+++ b/server/ptrace.c
@@ -109,7 +109,7 @@
 }
 
 /* handle a SIGCHLD signal */
-void sigchld_handler()
+void sigchld_callback(void)
 {
     int pid, status;