Update version to SNAPSHOT

[David Blevins]

I don't know what you anticipate the next version of OpenJPA to be,  
but it would be really great if we could get some snapshots out there  
for other projects to include in their maven2 builds.  Right now the  
version in the pom.xml 0.9.0 which wouldn't fly.  Something like  
0.9.1-SNAPSHOT or 1.0-SNAPSHOT, etc., would be better.

Thoughts?
-David