Import GInitable, GSocket and dependencies from gnio

This adds:
GInitable - failable object constructor interface
GAsyncInitable - async failable object constructor interface
GSocket - Platform independent lowlevel berkely socket style object
GSocketControlMessage - For passing control messages over GSocket
GUnixFDMessage - unix fd passing socket control message

Some changes were done during the import from gnio to make things
work in glib. For instance, types were moved to other headers, header
file boiler plate were updated to glib style and gio.symbols stuff
was added.

gio/gioerror.c

@@ -194,6 +194,12 @@ g_io_error_from_errno (gint err_no)
       break;
 #endif
 
+#ifdef EADDRINUSE
+    case EADDRINUSE:
+      return G_IO_ERROR_ADDRESS_IN_USE;
+      break;
+#endif
+
     default:
       return G_IO_ERROR_FAILED;
       break;