pgsql: Merge two copies of tuple-building code in pltcl.c.

Merge two copies of tuple-building code in pltcl.c.

Make pltcl_trigger_handler() construct modified tuples using
pltcl_build_tuple_result(), rather than its own copy of essentially
the same logic. This results in slightly different message wording for
the error cases, and in one case a different SQLSTATE, but it seems
unlikely that any existing applications are depending on any of those
details.

While at it, fix a typo in commit 26abb50c4: pltcl_build_tuple_result was
applying encoding conversion in the wrong direction. That would be a
back-patchable bug fix, except the code hasn't shipped yet.

Jim Nasby, reviewed by me

Discussion: https://postgr.es/m/d2c6425a-d9e0-f034-f774-4a872c234d89@BlueTreble.com

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/de5fed0d0c704e3d1a928bf420663319d898cee4

Modified Files
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src/pl/tcl/pltcl.c | 113 ++++++++++++++++++-----------------------------------
1 file changed, 39 insertions(+), 74 deletions(-)