pgsql: Mention in the docs that temporary/non-temp tables can not share

Log Message:
-----------
Mention in the docs that temporary/non-temp tables can not share
referential integrity relationships.

Modified Files:
--------------
pgsql/doc/src/sgml/ref:
create_table.sgml (r1.94 -> r1.95)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/create_table.sgml.diff?r1=1.94&r2=1.95)