TestFileEnvironment._find_exe broken on Windows
(Ported from http://trac.pythonpaste.org/pythonpaste/ticket/358)
The _find_exe() method of TestFileEnvironment? is broken on Windows because of Windows' automagic executable extensions: running "svn" might actually run "svn.exe" or "svn.bat" or probably other things I don't have a clue about.
%PATHEXT% is the environment variable needed to fix this properly.