Improve ForkRunner to fork() as expected

[christianhujer]

Currently, the AceUnit_ForkRunner.c file forks the individual method calls but not the fixture structure.

It should fork for the fixture structure, like this:

fork() {
    beforeAll();
    for (testCase in testCases) {
        fork() {
            beforeEach();
            fork() {
                testCase();
            }
            afterEach();
        }
    }
    afterAll();
}