Indentation of guards does not work sensibly with haskell-indentation

[jstolarek]

Say I have:

foo aX

where X denotes cursor position. I press Enter, type | to start a guard and press Tab to indent it:

foo a
  |X

So far so good. Now I type in a guard, press Enter, type =:

foo x
  | True
    =X

In this setting pressing Tab removes all indentation before =:

foo x
  | True
=X

Subsequent presses of Tab do not indent the code. Expected indentation:

foo x
  | True
  =X