fix scons problems with old files lying around
fix scons problems with old files lying around

This fixes a bug where strokes were not updated on canvas until the
canvas was moved - of course, only if you had old .so files lying
around. Users had to solve this with "git clean -xf" before.

(Ideally, old .so files shouldn't be used even if they are there.)

Clean up more old cruft when running "scons -c".

Problem was reported here for example:
http://forum.intilinux.com/mypaint-development-and-suggestions/new-cursor-from-git/msg11871/#msg11871
I could reproduce that by building many old versions, and then master.

achadwick/libmypaint,b3sigma/libmypaint,achadwick/libmypaint,b3sigma/libmypaint,b3sigma/libmypaint,achadwick/libmypaint,achadwick/libmypaint