Use pread/pwrite everywhere to avoid changing the file position while
the client is using it.
Get rid of the no longer used truncate_file request.

diff --git a/server/signal.c b/server/signal.c
index 593b88a..99d9b82 100644
--- a/server/signal.c
+++ b/server/signal.c
@@ -243,6 +243,8 @@
     action.sa_handler = do_sigterm;
     sigaction( SIGQUIT, &action, NULL );
     sigaction( SIGTERM, &action, NULL );
+    action.sa_handler = SIG_IGN;
+    sigaction( SIGXFSZ, &action, NULL );
 #ifdef HAVE_SIGINFO_T_SI_FD
     action.sa_sigaction = do_sigio;
     action.sa_flags = SA_SIGINFO;