Fix indentation for some forms.

- `do-while` should indent the same as `while`.  The same goes for `do-until`.

- `if` should *not* indent as in Emacs Lisp, i.e. it should not do this:

  ```
  (if test
      then
    else)
  ```

  It now does the following:

  ```
  (if test
      then
      else)
  ```

  or, more generally,

  ```
  (if test
      then
      test-2
      then-2
      ...
      otherwise)
  ```

  which agrees with the `cond`-y nature of newLISP's `if`. (On this, see http://www.newlispfanclub.alh.net/forum/viewtopic.php?f=15&t=4383.)