add FileEdit.isDirectory and fix @link tags in scripting doc

[dogboydog]

No description provided.

[bjorn]

While you're at it, could you also document the FileEdit.filter property? :-)

Something like:

When specified, only files that match the filter are shown. The filter is given in a format like "Images (*.png *.xpm *.jpg)". If you want multiple filters, separate them with ';;', for example:

 "Images (*.png *.xpm *.jpg);;Text files (*.txt);;XML files (*.xml)"

[bjorn]

Thanks! :-)