pgsql: Update FAQ item: <H3 id="item3.6">3.6) What is the upgrade

Log Message:
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Update FAQ item:

<H3 id="item3.6">3.6) What is the upgrade process for
PostgreSQL?</H3>

to reference both versioning and specific upgrade instructions.

Modified Files:
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pgsql/doc:
FAQ (r1.425 -> r1.426)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/FAQ.diff?r1=1.425&amp;r2=1.426)
pgsql/doc/src/FAQ:
FAQ.html (r1.381 -> r1.382)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/FAQ/FAQ.html.diff?r1=1.381&amp;r2=1.382)