ROL-1739 add a DB constraint?

[Glen Mazza]

Hi Team, re: https://issues.apache.org/jira/browse/ROL-1739, in 2008 a 
user reported a data error in the weblog-entry-tag-aggregate table that 
probably would have been immediately caught if we had a DB constraint 
preventing it.  Namely, a unique key constraint on the weblog and the 
tag name.  Since the purpose of this constraint is primarily to trap and 
fix a potential error in Roller, I wouldn't mind adding it just to the 
createdb.vm script but *not* the 500-to-510 migration script.  This way 
anybody with an invalid tag table can still do the upgrade (upgrades are 
going to be complex enough without this extra curve ball), while we'll 
find out about the tag aggregate table error, if it still exists, from 
new Roller users.

Alternatively, we can also just omit adding this constraint and closing 
the matter as a won't fix (especially if we're reasonably confident the 
tag aggregate table error has been fixed since then.) What I wouldn't 
want to do is keep this issue open anymore -- one way or another, let's 
get this one closed.  WDYT?

Regards,
Glen