Passing col parameter to add_BBands (in chart.Posn) generates error

e.g. TA = 'add_BBands(n=10, col=4)'

```
error in evaluating the argument 'x' in selecting a method for function 'print': Error in plot.xy(xy.coords(x, y), type = type, ...) :
formal argument "col" matched by multiple actual arguments
```

Perhaps because col was not a formal parameter in the following code

```
lenv$plot_bbands <- function(x, n, maType, sd, on, ...) {
```

as compared to code of add_SMA

```
lenv$add_sma <- function(x, n, col, ...) {
```