pgsql: Fix some portability issues in isolation regression test driver.

Fix some portability issues in isolation regression test driver.

Remove random system #includes in favor of using postgres_fe.h.  (The
alternative to that is letting this module grow its own configuration
testing ability...)

Also fix the "make clean" target to actually clean things up.

Per local testing.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/eff223ffd74eed268f35d693462969f7f75632d2

Modified Files
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src/test/isolation/Makefile          |    4 ++--
src/test/isolation/isolation_main.c  |    2 +-
src/test/isolation/isolationtester.c |    6 ++----
src/test/isolation/specparse.y       |    5 +----
4 files changed, 6 insertions(+), 11 deletions(-)