Adjust a repository layer test to properly abort each failed commit, to obey the editor driving rules.
This test was working fine by itself but made too many assumptions, and so would fail when introducing editor 'shims' into the commit editor code path, as is typically done when testing Ev2 (or Ev3) code. That's how I found the problem, while working on the 'move-tracking-2' branch.
* subversion/tests/libsvn_repos/repos-test.c (fwcc_prepare): New, extracted from ... (filename_with_control_chars): ... here. Start up and tear down each failed editor drive separately instead af assuming that the expected failure would be reported immediately and that the editor would still be usable after the failure.