Sketches using processing libraries may fail to find library

[Martin Prout]

Discovered on a fresh install of processing-3.0a4 (no other versions installed). Path to sketchbook in preferences.txt is set thus:-
sketchbook.path.three=/home/tux/sketchbook

ruby-processing expects requires:-

sketchbook.path=/home/tux/sketchbook

Solution use processing-2.2.1 for foreseeable future, or:-

1. edit preferences.txt.
2. Set sketchbook_path in .rp5rc

[Martin Prout]

Fix as long as preferences.txt is stable.
d8147a1