The nixpkgs-unstable channel's programs.sqlite was used to identify
packages producing exactly one binary, and these automatically added
to their package definitions wherever possible.
The Sourceforge ZIP URLs aren't stable. They (sometimes?) disappear
and throw 404. Probably until someone requests the file to be
generated from the UI. This made the build of xflr5 fail. By using the
SVN checkout we should be on the safer side.
This updates to the latest version. Unfortunately the project stopped
publishing source tarballs in the way we used to consume them. We've
to retrieve a source snapshot from sourceforge's SVN service instead.
The alternative would be a subversion checkout which I don't think is
any better or worse.
