(second try for this, the first one I posted through Gmane disappeared)

Attached is a patch which:

- adds optional SEMICOLONS and KEEP-EMPTY to `url-build-query-string' to
  separate parameters with semicolons and to keep empty values

- fixes `url-parse-query-string' to understand the '=' is not required
  in a parameter

- adds ERT tests for `url-build-query-string' and
  `url-parse-query-string'

Ian, if you could look it over, I'd appreciate it.  In particular if you
think KEEP-EMPTY should be the default or if you see any other problems...

Thanks
Ted