Fix a bug and a flaw with auto-end introduced in the revamp.

- ruby-forward-sexp is inappropriate here because it moves the cursor
  past the keyword.

- Fix a reversed looking-back check in
  ruby-electric--block-beg-keyword-at-point-p.

- Do not add end again if space or return is hit repeatedly after a
  block beginning keyword.
Bump version to 2.0.1.