Fix some path and URL handling in the test suite, to enable it to work better

Fix some path and URL handling in the test suite, to enable it to work better
with paths containing spaces. Specifically, the test suite should now work in
a work_dir called "svn test work" rather than "svn-test-work" if desired.

* subversion/tests/cmdline/svntest/main.py
  (pathname2url, url2pathname): New functions.
  (test_area_url): Properly URL-encode the path part.
  (Sandbox._set_name, Sandbox.add_repo_path): Properly URL-encode the path
    part of the new URL.
  (run_tests): Properly URL-encode the path part of pristine_url.

* subversion/tests/cmdline/svntest/tree.py
  (build_tree_from_skipped): Don't reject a path that contains a space.

git-svn-id: http://svn.apache.org/repos/asf/subversion/trunk/subversion/tests/cmdline@873681 13f79535-47bb-0310-9956-ffa450edef68