pgsql: Update installation wording for an upgrade to state that

Log Message:
-----------
Update installation wording for an upgrade to state that dump/restore
should not be done, per Peter.

Modified Files:
--------------
pgsql/doc/src/sgml:
installation.sgml (r1.276 -> r1.277)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/installation.sgml.diff?r1=1.276&r2=1.277)