pgsql: Make plpython_unicode regression test work in more database enco

Make plpython_unicode regression test work in more database encodings.

This test previously used a data value containing U+0080, and would
therefore fail if the database encoding didn't have an equivalent to
that; which only about half of our supported server encodings do.
We could fall back to using some plain-ASCII character, but that seems
like it's losing most of the point of the test. Instead switch to using
U+00A0 (no-break space), which translates into all our supported encodings
except the four in the EUC_xx family.

Per buildfarm testing. Back-patch to 9.1, which is as far back as this
test is expected to succeed everywhere. (9.0 has the test, but without
back-patching some 9.1 code changes we could not expect to get consistent
results across platforms anyway.)

Branch
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REL9_2_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/658fad7ff0d1caa3b3fcb548fd6780c563f7ead6

Modified Files
--------------
src/pl/plpython/expected/plpython_unicode.out | 17 +++++++++++------
src/pl/plpython/sql/plpython_unicode.sql | 11 ++++++++---
2 files changed, 19 insertions(+), 9 deletions(-)