Log Message:
-----------
Change a couple of "can't happen" error messages to be a shade more
verbose when they do happen. The "left link changed unexpectedly"
one in particular has been seen more than once in the field.
Modified Files:
--------------
pgsql/src/backend/access/nbtree:
nbtpage.c (r1.86 -> r1.87)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/nbtree/nbtpage.c.diff?r1=1.86&r2=1.87)