RSyntaxTextArea and AutoComplete have independent versioning

D'oh...

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Backport IJ2's Script Editor's changes to support newer RSyntaxTextArea

Their API changed a little bit from the ancient version we used to use.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>