[PATCH] big test separation POC

Dear hackers,

Per various discussion about the potential impact of Robins non regression 
tests, here is a poc patch to separate big tests from others.

"paralle_schedule" holds usual tests, "big_schedule" holds big tests.

The makefile derives serial_schedule, parallel_big_schedule and 
serial_big_schedule from the above descriptions.

Then: - make check in regress does usual tests - make bigcheck in regress does both usual and big tests

I'm not sure about what happens under vpath.

I have no opinion about what should be considered a big test.

-- 
Fabien.