skip test_setup without fork

skip test_setup without fork

This test is run 3 times, and each run attempts to change some global
memory. If using fork, each test has the same global memory. However,
without fork subsequent tests observe the changed global memory from
previous tests. Disabling all but the first run if there is no fork(),
and the test is invalid without fork.

git-svn-id: svn+ssh://svn.code.sf.net/p/check/code/trunk@769 64e312b2-a51f-0410-8e61-82d0ca0eb02a