Add value field to @Nonnull annotation for improved readability

[GoogleCodeExporter]

I recommend that we add a "value" field to annotations accepting the 
javax.annotation.meta.When value.  This allows more succinct (and I feel 
readable) code such as:

@Nonnull(When.ALWAYS) instead of @Nonnull(when = When.ALWAYS) code.  The 
alternative is to import the fields from When, yielding @Nonnull(when=ALWAYS), 
which is about equivalent, but I feel the value option is more idiomatic, where 
available.

Original issue reported on code.google.com by [email protected] on 1 Jun 2011 at 8:00