Inconsistent error message wording for REINDEX CONCURRENTLY

In view of the REINDEX-on-pg_class kerfuffle that we're currently
sorting through, I was very glad to see that the concurrent reindex
code doesn't even try:

regression=# reindex index concurrently pg_class_oid_index;
psql: ERROR:  concurrent reindex is not supported for catalog relations
regression=# reindex table concurrently pg_class; 
psql: ERROR:  concurrent index creation on system catalog tables is not supported

It'd be nice though if those error messages gave the impression of having
been written on the same planet.

(It might be worth comparing wording of other errors-in-common between
what are evidently two completely different code paths...)

			regards, tom lane