amcheck: Remove duplicate XID/MXID bounds checks.
Commit
3b6c1259f9ca8e21860aaf24ec6735a8e5598ea0 resulted in the same
xmin and xmax bounds checking being performed in both check_tuple()
and check_tuple_visibility(). Remove the duplication.
While at it, adjust some code comments that were overlooked in that
commit.
Mark Dilger
Discussion: http://postgr.es/m/
AC5479E4-6321-473D-AC92-
5EC36299FBC2@enterprisedb.com