create index concurrently docs ...

In reading over the caveats regarding create index concurrently, I
think it'd be nice to see an example of what the return result will
be if an 'invalid' index is created so a dba who read the docs night
recognize the error, as well as for searchengine fodder to find out
what to do real fast if such an error happens to them.

Something around this paragraph in http://www.postgresql.org/docs/
current/static/sql-createindex.html#SQL-CREATEINDEX-CONCURRENTLY:

"If a problem arises during the second scan of the table, such as a
uniqueness violation in a unique index, the CREATE INDEX command will
fail but leave behind an "invalid" index."

Thanks!
----
James Robinson
Socialserve.com