[eclipselink-dev] Fix for bug 237281 - EclipseLink throws InstantiationE

[Tom Ware <tom.ware@xxxxxxxxxx>]

https://bugs.eclipse.org/bugs/show_bug.cgi?id=237281

Checked in.

Reviewed by Gordon Yorke - Note: We disagree about what the behavior should be 
for the case where the non-entity subclass is being persisted by cascade, but 
have agreed the fix is ok to check-in as is.

Some additional review by James Sutherland

Added: testExceptionForPersistNonEntitySubclass and 
testEnabledPersistNonEntitySubclass to EntityManagerJUnitTestSuite