Unwrapping paragraphs

Hello …

I am trying to unwrap some text and can’t seem to find a way to do so, eg. by using a regex. I would like to replicate what Textmate does with ctrl-Q

Example

la
di
da

la
di
da

should become:

la di da

la di da

Important is, that the double newline between the paragraphs remains. The file will run through ConTexT, and this separates paragraphs.

Thanks for any pointers.
Martin