pgsql: Disallow referential integrity actions from being deferred; only

Log Message:
-----------
Disallow referential integrity actions from being deferred; only the
NO ACTION check is deferrable.  This seems to be a closer approximation
to what the SQL spec says than what we were doing before, and it prevents
some anomalous behaviors that are possible now that triggers can fire
during the execution of PL functions.
Stephan Szabo.

Modified Files:
--------------
    pgsql/doc/src/sgml:
        ddl.sgml (r1.30 -> r1.31)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ddl.sgml.diff?r1=1.30&r2=1.31)
    pgsql/doc/src/sgml/ref:
        create_table.sgml (r1.84 -> r1.85)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/create_table.sgml.diff?r1=1.84&r2=1.85)
    pgsql/src/backend/commands:
        tablecmds.c (r1.135 -> r1.136)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/tablecmds.c.diff?r1=1.135&r2=1.136)
        trigger.c (r1.172 -> r1.173)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/trigger.c.diff?r1=1.172&r2=1.173)