(py-block-comment-prefix): Remove trailing space.  Also explain that this string should not end with whitespace.
(py-block-comment-prefix): Remove trailing space.  Also explain that
this string should not end with whitespace.

(py-compute-indentation): Append whitespace regexp to
py-block-comment-prefix so that any combination of intervening
whitespace will be recognized.

sk-/python2.7-type-annotator,sk-/python2.7-type-annotator,sk-/python2.7-type-annotator