Make parse errors meaningful.

This makes the error displays on a bad setup.cfg value go from:

error in setup command: Error parsing setup.cfg: IOError: 2

to

error in setup command: Error parsing setup.cfg: IOError: No such file or
directory: 'README'

Which makes debugging eversomuch better.

pbr/d2to1/core.py

@@ -47,8 +47,7 @@ def d2to1(dist, attr, value):
     except:
         e = sys.exc_info()[1]
         raise DistutilsSetupError(
-            'Error parsing %s: %s: %s' % (path, e.__class__.__name__,
-                                          e.args[0]))
+            'Error parsing %s: %s: %s' % (path, e.__class__.__name__, e))
 
     # Repeat some of the Distribution initialization code with the newly
     # provided attrs