[GT] Fix to I:Generic:ByName

["Weigert, Thomas" <weigert AT mst.edu>]

This indicator had a bug which made it somewhat difficult to predict
when it would work and when not. A good example is the rewrite of DSS
that kw did. He was forced to redo the unneeded computations when
applying the second smoothing:

    $self->{'ema1'} = GT::Indicators::EMA->new([
$self->{'args'}->get_arg_names(2), $sto1 ]);
    $self->{'ema2'} = GT::Indicators::EMA->new([
$self->{'args'}->get_arg_names(3),
        "{I:EMA @{[$self->{'ema1'}->{'args'}->get_arg_names()]}}" ]);

Ideally, ema2 should just use ema1, as follows:

    $self->{'ema2'} = GT::Indicators::EMA->new([
$self->{'args'}->get_arg_names(3),
        "{I:Generic:ByName " . $self->{'ema1'}->get_name . "}" ]);

That way, the first smoothing is not computed twice, and it is also
easier to understand and has more reuse.

However, that did not work due to the bug mentioned.

The attached indicator fixes this problem. As the construction of
ArgTree is somewhat brittle in GT, please advise of any problems you run
into with this indicator if you do. I'll take care of it.

Cheers, Th.

Attachment: ByName.pm
Description: ByName.pm