Add socket path to IPC errors for more clarity

`Error calling bind() on socket: Permission denied` is not a clear error
message, because the socket that needs to be checked is not mentioned.

New error message:
`Error calling bind() on socket /tmp/luakit-ipc...: Permission denied`

ipc.c

@@ -129,10 +129,10 @@ web_extension_connect_thread(gpointer UNUSED(data))
     unlink(local.sun_path);
 
     if (bind(sock, (struct sockaddr *)&local, len) == -1)
-        fatal("Error calling bind(): %s", strerror(errno));
+        fatal("Error calling bind() on socket %s: %s", path, strerror(errno));
 
     if (listen(sock, 5) == -1)
-        fatal("Error calling listen(): %s", strerror(errno));
+        fatal("Error calling listen() on socket %s: %s", path, strerror(errno));
 
     g_mutex_lock(&socket_path_lock);
     socket_path = path;