This fixes an indentation bug reported by Jeremy when seeing multiple
list comprehensions like so:

    [x for x in seq
     if blah(x)]

    # ...

    [y for y in seq
     if blah(y)]

The reason this broke is because this regexp caused the "find a safe
parsing start location higher up in the file" test to erroneously find
the if in the listcomp.  I think the other keywords in this regexp are
fine and good enough.

After a weekend of testing, I can't find any adverse effects.