set_nonfatal_assertions

Changes the behaviour of the various `g_assert_*()` macros, assert_expected_messages and the various `g_test_trap_assert_*()` macros to not abort to program, but instead call fail and continue.

(This also changes the behavior of fail so that it will not cause the test program to abort after completing the failed test.)

Note that the assert_not_reached and assert macros are not affected by this.

This function can only be called after init.