pgsql: Have thread_test create its test files in the current directory,

Have thread_test create its test files in the current directory, rather
than /tmp.  Also cleanup C defines and add comments.

Per report by Alex Soto

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/6cc08e703bb078ee1e8d183caf4596d62bf12bf7

Modified Files
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src/test/thread/thread_test.c |  138 +++++++++++++----------------------------
1 files changed, 43 insertions(+), 95 deletions(-)