Log Message:
-----------
Improve error messages and add comment
Modified Files:
--------------
pgsql/src/backend/access/gist:
gistxlog.c (r1.6 -> r1.7)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/gist/gistxlog.c.diff?r1=1.6&r2=1.7)