pgsql: Fix getTypeIOParam to support type record[].

Fix getTypeIOParam to support type record[].

Since record[] uses array_in, it needs to have its element type passed
as typioparam. In HEAD and 9.1, this fix essentially reverts commit
9bc933b2125a5358722490acbc50889887bf7680, which was a hack that is no
longer needed since domains don't set their typelem anymore. Before
that, adjust the logic so that only domains are excluded from being
treated like arrays, rather than assuming that only base types should
be included. Add a regression test to demonstrate the need for this.
Per report from Maxim Boguk.

Back-patch to 8.4, where type record[] was added.

Branch
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REL9_1_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/ac3dcca22e967ac4a899c4534b4b1c8e807ff71e

Modified Files
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src/backend/utils/cache/lsyscache.c | 5 ++---
src/test/regress/expected/polymorphism.out | 21 +++++++++++++++++++++
src/test/regress/sql/polymorphism.sql | 15 +++++++++++++++
3 files changed, 38 insertions(+), 3 deletions(-)