Ignore SIGPIPE.

This doesn't matter for regular Babel, but it breaks the babel-local-interface
branch, which uses a TCP socket for communicating with the GUI.

babel.c

@@ -884,6 +884,12 @@ init_signals(void)
     sa.sa_flags = 0;
     sigaction(SIGINT, &sa, NULL);
 
+    sigemptyset(&ss);
+    sa.sa_handler = SIG_IGN;
+    sa.sa_mask = ss;
+    sa.sa_flags = 0;
+    sigaction(SIGPIPE, &sa, NULL);
+
     sigemptyset(&ss);
     sa.sa_handler = sigdump;
     sa.sa_mask = ss;