Log Message:
-----------
Add note that TRUNCATE is not MVCC-safe.
Modified Files:
--------------
pgsql/doc/src/sgml/ref:
truncate.sgml (r1.22 -> r1.23)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/truncate.sgml.diff?r1=1.22&r2=1.23)