Notice if we lose the RTLSDR device and reconnect.

Fix some of the more glaring pthread bugs.

dump1090.h

@@ -311,7 +311,7 @@ struct {                             // Internal state
     int             exit;            // Exit from the main loop when true
 
     // RTLSDR
-    int           dev_index;
+    char *        dev_name;
     int           gain;
     int           enable_agc;
     rtlsdr_dev_t *dev;