Label additions

As I've mentioned in the last post, Label::adopt() now accepts the rowops from other labels that belong to the other units without complaining.

But there are more refinements. The next one was already shown in the examples but I didn't draw the attention to it:

$lb2 = $lb1->makeChained($name, \&subClear, \&subExec, @args);

It creates a new label by chaining it from another existing label. The arguments are very much the same as in Unit::makeLabel(), only there is no need to specify the row type for the new label (nor obviously the Unit), these are taken from the original label.

Another one allows to check whether the label has been already cleared:

$result = $lb->isCleared();

This method has been available in C++ all along but not it's exported to Perl too.