Added UNIX implementation of both timers and sockets. Timers should work,

sockets were tested only in TCP mode. main.c now contains some test
cases for socket code.

sysdep/unix/unix.h

@@ -0,0 +1,17 @@
+/*
+ *	BIRD -- Declarations Common to Unix Port
+ *
+ *	(c) 1998 Martin Mares <mj@ucw.cz>
+ *
+ *	Can be freely distributed and used under the terms of the GNU GPL.
+ */
+
+#ifndef _BIRD_UNIX_H_
+#define _BIRD_UNIX_H_
+
+/* io.c */
+
+void io_init(void);
+void io_loop(void);
+
+#endif