fill-paragraph: multi-level indentations / enumerations?

[Markus Dehmann]

The fill-paragraph function in my emacs 21.4.1 (on linux) is missing
some basic understanding of multi-level indentations or enumerations.

If I am in text-mode and I type
(1) blah blah blah blah blah blah blah blah blah blah blah blah blah
    blah blah blah
    (1.1) blah blah blah blah blah blah blah blah blah blah blah blah
blah blah

and fill-paragraph will change it to this:
(1) blah blah blah blah blah blah blah blah blah blah blah blah blah
    blah blah blah (1.1) blah blah blah blah blah blah blah blah blah
    blah blah blah blah blah

But of course I want the correct indentation instead:
(1) blah blah blah blah blah blah blah blah blah blah blah blah blah
    blah blah blah
    (1.1) blah blah blah blah blah blah blah blah blah blah blah blah
blah
          blah

How can I do that? Can I modify the fill-paragraph function so that it
understands hierarchical indentations? My emacs version on the Mac
does it, so there obviously is a way to get it.

Thanks,
Markus