pgsql: Tweak planner to use a minimum size estimate of 10 pages for a

Log Message:
-----------
Tweak planner to use a minimum size estimate of 10 pages for a
never-yet-vacuumed relation. This restores the pre-8.0 behavior of
avoiding seqscans during initial data loading, while still allowing
reasonable optimization after a table has been vacuumed. Several
regression test cases revert to 7.4-like behavior, which is probably
a good sign. Per gripes from Keith Browne and others.

Modified Files:
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pgsql/src/backend/optimizer/util:
plancat.c (r1.100 -> r1.101)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/util/plancat.c.diff?r1=1.100&r2=1.101)
pgsql/src/test/regress/expected:
join.out (r1.22 -> r1.23)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/join.out.diff?r1=1.22&r2=1.23)
polymorphism.out (r1.6 -> r1.7)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/polymorphism.out.diff?r1=1.6&r2=1.7)
rules.out (r1.95 -> r1.96)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/rules.out.diff?r1=1.95&r2=1.96)