upgrader: fix / reformat comments

borg/upgrader.py

@@ -87,17 +87,15 @@ class AtticRepositoryUpgrader(Repository):
                     segment.seek(0)
                     segment.write(new_magic)
                 else:
-                    # remove the hardlink and rewrite the file. this
-                    # works because our old file handle is still open
-                    # so even though the file is removed, we can still
-                    # read it until the file is closed.
+                    # rename the hardlink and rewrite the file. this works
+                    # because the file is still open. so even though the file
+                    # is renamed, we can still read it until it is closed.
                     os.rename(filename, filename + '.tmp')
                     with open(filename, 'wb') as new_segment:
                         new_segment.write(new_magic)
                         new_segment.write(segment.read())
                     # the little dance with the .tmp file is necessary
-                    # because Windows won't allow overwriting an open
-                    # file.
+                    # because Windows won't allow overwriting an open file.
                     os.unlink(filename + '.tmp')
 
     def find_attic_keyfile(self):