Move to Eclipse 3.3 at 3.3M5

[David Aspinall <da+pgtrac@…>]

3.3M5 stable is due 9th February. We should migrate code and development to that version.

Our main distribution format is the Proof General Eclipse product, and we expect most users will use this rather than adding a plugin to their existing Eclipse install. This means we can be more speedy about shifting to new versions of the platform. It lets us fix compatibility issues early, and potentially feed suggestions for API improvement upstream.

Probably our products built on milestone releases should be regarded as beta.

Drawback/limitation: tools we are using for development may not be upgraded so quickly. (Are there any show stoppers?)