pgsql: I've had this small patch in my local tree for a while.

Log Message:
-----------
I've had this small patch in my local tree for a while. It documents
new commands which may make an SPI call fail.

Alvaro Herrera

Modified Files:
--------------
pgsql/doc/src/sgml:
spi.sgml (r1.41 -> r1.42)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/spi.sgml.diff?r1=1.41&r2=1.42)