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
------
master

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

Modified Files
--------------
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(-)