pgsql: Fix an old thinko in SS_make_initplan_from_plan, which is used

Log Message:
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Fix an old thinko in SS_make_initplan_from_plan, which is used when optimizing
a MIN or MAX aggregate call into an indexscan: the initplan is being made at
the current query nesting level and so we shouldn't increment query_level.
Though usually harmless, this mistake could lead to bogus "plan should not
reference subplan's variable" failures on complex queries. Per bug report
from David Sanchez i Gregori.

Tags:
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REL8_2_STABLE

Modified Files:
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pgsql/src/backend/optimizer/plan:
subselect.c (r1.112.2.1 -> r1.112.2.2)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/plan/subselect.c.diff?r1=1.112.2.1&r2=1.112.2.2)
pgsql/src/test/regress/expected:
subselect.out (r1.14 -> r1.14.2.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/subselect.out.diff?r1=1.14&r2=1.14.2.1)
pgsql/src/test/regress/sql:
subselect.sql (r1.9 -> r1.9.2.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/subselect.sql.diff?r1=1.9&r2=1.9.2.1)