Pattern coverage

[Brian Goetz]

I've put a document at

http://cr.openjdk.java.net/~briangoetz/eg-attachments/Coverage.pdf

which outlines a formal model for pattern coverage, including record 
patterns and the effects of sealing.  This refines the work we did 
earlier.  The document may be a bit rough so please let me know if you 
spot any errors.  The approach here should be more amenable to 
specification than the previous approach.