oceani: updates for new approach to parsing indents.

Now that IN is a valid stand-alone token, it makes sense to change the
grammar for ocean.
We don't need the ':' before an indent if there is some other terminal
there.  So:

  while
     statements
  do
     statements

doesn't require any ':'.
We use the ':' to separate an expression from following statements,
in 'if' and 'while' and 'case'.

Signed-off-by: NeilBrown <neil@brown.name>