pgsql: Remove prepared transactions from main isolation test schedule.

Remove prepared transactions from main isolation test schedule.

There is no point in running this test when prepared transactions are disabled,
which is the default. New make targets that include the test are provided. This
will save some useless waste of cycles on buildfarm machines.

Backpatch to 9.1 where these tests were introduced.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/ae55d9fbe3871a5e6309d9b91629f1b0ff2b8cba

Modified Files
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src/test/isolation/Makefile           |   10 ++++++++++
src/test/isolation/isolation_schedule |    1 -
2 files changed, 10 insertions(+), 1 deletions(-)