Replace old except syntax with new one

Drops Python 2.5 support

dataset/freeze/app.py

@@ -91,7 +91,7 @@ def freeze_export(export, result=None):
         serializer_cls = get_serializer(export)
         serializer = serializer_cls(export, query)
         serializer.serialize()
-    except ProgrammingError, pe:
+    except ProgrammingError as pe:
         raise FreezeException("Invalid query: %s" % pe)
 
 
@@ -110,7 +110,7 @@ def main():
                 continue
             log.info("Running: %s", export.name)
             freeze_export(export)
-    except FreezeException, fe:
+    except FreezeException as fe:
         log.error(fe)
 
 if __name__ == '__main__':

dataset/freeze/config.py

@@ -31,10 +31,10 @@ class Configuration(object):
             fh = open(file_name, 'rb')
             try:
                 self.data = loader.load(fh)
-            except ValueError, ve:
+            except ValueError as ve:
                 raise FreezeException("Invalid freeze file: %s" % ve)
             fh.close()
-        except IOError, ioe:
+        except IOError as ioe:
             raise FreezeException(unicode(ioe))
 
     @property