tests: cleanup of svn url handling The subversion tests used different tricks to create properly encoded URLs, partly due to partial support for different ways of running the tests on windows. Now we only need/support one way of running the tests on windows. Windows URLs should look like 'file:///c:/foo%20bar' and on Unix platforms like 'file:///tmp/baz'. 'pwd' in the test framework will on Windows emit paths like 'c:/foo bar'. Explicit handling of backslashes in paths is thus no longer needed and is removed. Paths on windows do however need an extra '/' compared to other platforms. This change makes test-subrepo-svn.t pass on windows with msys. Other tests might need more work.