Fix enable-remote-debug CLI spec.
Implement SubversionClient and SubversionClientException classes.
Add support for descriptions/epilogs.
Implement initial scaffolding for multi-component repository support.
Add new errors for enforcing multi-component repositories.
Implement initial logic for enforcing multi-component repositories.
Add chdir (from ctk).
Add selftest-base-dir to config.
Improve testing infrastructure.

    - Handle multiple modules.
    - Respect -q/--quiet.
Implement try_remove_dir and try_remove_dir_atexit.
Add `shell` keyword to ProcessWrapper, fix Popen() usage.

The `exe=self.executable` isn't necessary.
Introduce evn.exe: helper module for calling svn*, evnadmin.
Separate selftest/unittest.
Fix component-depth logic.
Another round of improvements for testing scaffolding.
Add singleton config support (from ctk).
Fix SubversionClient.build_command_line's ci/commit logic.
Implement build_tree().
Add directory tree building support to TestRepo.
Make it obvious when any failures occur with a big ugly message at the end of the run.