command.c improve err msg for bad jog request

ref: taskintf.cc:emcJogCont(),emcJogIncr(),emcJogAbs(),emcJogStop()
if  jjogmode ==> emcmotCommand.axis  = -1 (for a joint jog request)
if !jjogmode ==> emcmotCommand.joint = -1 (for a axis  jog request)

so detect that:
    a joint jog has been requested when current mode is teleop
or
    a axis coordinate jog has been requested when current mode is NOT teleop
and make messages less opaque

Note: maintain detection of unexpected conditions such as
      simultaneous negative axis_num *and* negative joint_num

src/emc/motion/command.c

@@ -448,11 +448,17 @@ void emcmotCommandHandler(void *arg, long period)
             || emcmotCommand->command == EMCMOT_JOG_ABS
            ) {
            if (GET_MOTION_TELEOP_FLAG() && axis_num < 0) {
-               emsg = "command.com teleop bad axis_num";
+               emsg = "command.com teleop: unexpected negative axis_num";
+               if (joint_num >= 0) {
+                   emsg = "Mode is TELEOP, cannot jog joint";
+               }
                abort = 1;
            }
            if (!GET_MOTION_TELEOP_FLAG() && joint_num < 0) {
-               emsg = "command.com !teleop bad joint_num";
+               emsg = "command.com !teleop: unexpected negative joint_num";
+               if (axis_num >= 0) {
+                   emsg = "Mode is NOT TELEOP, cannot jog axis coordinate";
+               }
                abort = 1;
            }
            if (GET_MOTION_TELEOP_FLAG()) {
@@ -468,16 +474,13 @@ void emcmotCommandHandler(void *arg, long period)
         if (abort) {
           switch (emcmotCommand->command) {
           case EMCMOT_JOG_CONT:
-               rtapi_print_msg(RTAPI_MSG_ERR,"JOG_CONT %s cmd=%d\n",
-                               emsg,emcmotCommand->command);
+               rtapi_print_msg(RTAPI_MSG_ERR,"JOG_CONT %s\n",emsg);
                break;
           case EMCMOT_JOG_INCR:
-               rtapi_print_msg(RTAPI_MSG_ERR,"JOG_INCR %s cmd=%d\n",
-                               emsg,emcmotCommand->command);
+               rtapi_print_msg(RTAPI_MSG_ERR,"JOG_INCR %s\n",emsg);
                break;
           case EMCMOT_JOG_ABS:
-               rtapi_print_msg(RTAPI_MSG_ERR,"JOG_ABS %s cmd=%d\n",
-                               emsg,emcmotCommand->command);
+               rtapi_print_msg(RTAPI_MSG_ERR,"JOG_ABS %s\n",emsg);
                break;
           default: break;
           }