pgsql: Improve coverage of pltcl regression tests.

Improve coverage of pltcl regression tests.

Test composite-type arguments and the argisnull and spi_lastoid Tcl
commmands.  This stuff was not covered before, but needs to be exercised
since the upcoming Tcl object-conversion patch changes these code paths
(and broke at least one of them).

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/68c521eb92c3515e3306f51a7fd3f32d16c97524

Modified Files
--------------
src/pl/tcl/expected/pltcl_queries.out   | 47 +++++++++++++++++++++++++++++++++
src/pl/tcl/expected/pltcl_queries_1.out | 47 +++++++++++++++++++++++++++++++++
src/pl/tcl/expected/pltcl_setup.out     | 13 +++++++++
src/pl/tcl/sql/pltcl_queries.sql        | 15 +++++++++++
src/pl/tcl/sql/pltcl_setup.sql          | 18 +++++++++++++
5 files changed, 140 insertions(+)