Make format strings use named placeholders rather than %s/%r

Fixing some issues reported while updating roundup.pot to prep for
2.0.0 beta releases. Still more to do but....

Author: rouilj

roundup/backends/rdbms_common.py

@@ -545,8 +545,9 @@ def update_class(self, spec, old_spec, force=0):
             return 0
 
         if not self.config.RDBMS_ALLOW_ALTER:
-            raise DatabaseError(_('ALTER operation disallowed: %r -> %r.'% (
-                old_spec, new_spec)))
+            raise DatabaseError(_(
+                'ALTER operation disallowed: %(old)r -> %(new)r.'% {
+                    'old': old_spec, 'new': new_spec}))
 
         logger = logging.getLogger('roundup.hyperdb.backend')
         logger.info('update_class %s' % spec.classname)

roundup/scripts/roundup_server.py

@@ -499,7 +499,8 @@ def start_response(self, headers, response):
 
 def error():
     exc_type, exc_value = sys.exc_info()[:2]
-    return _('Error: %s: %s' % (exc_type, exc_value))
+    return _('Error: %(type)s: %(value)s' % {'type': exc_type,
+                                             'value': exc_value})
 
 
 def setgid(group):