fix borg.exe presence detection for python3.2

borg/testsuite/archiver.py

@@ -103,7 +103,7 @@ def exec_cmd(*args, archiver=None, fork=False, exe=None, **kw):
 try:
     exec_cmd('help', exe='borg.exe', fork=True)
     BORG_EXES = ['python', 'binary', ]
-except IOError as err:
+except (IOError, OSError) as err:
     if err.errno != errno.ENOENT:
         raise
     BORG_EXES = ['python', ]