pgsql: Update spoofing /tmp symlink instructions to be more specific

Log Message:
-----------
Update spoofing /tmp symlink instructions to be more specific about the
name of the needed symlink file.

Modified Files:
--------------
pgsql/doc/src/sgml:
runtime.sgml (r1.404 -> r1.405)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/runtime.sgml?r1=1.404&r2=1.405)