Two fixes for plpgsql.sgml

Hi,

This patch fixes two issues on plpgsql.sgml. Please review them
carefully, at least the second one. Thanks.

Regards.

PS : this patch should be in context diff if my .cvsrc is correctly set
up... at least, it doesn't look like my previous patch :)


-- 
Guillaume.
 http://www.postgresqlfr.org
 http://dalibo.com