'xfce-do-release' does not work on FreeBSD

xfce-do-release uses hard-coded make and sed, and therefore on FreeBSD native BSD versions of make and sed are used. Both BSD make and sed does not work as expected in xfce-do-release - it is not possible to build distribution (BSD make problem) and version numbers are invalid (sed problem). For testing purpose I replaced sed with gsed and make with gmake, which solved the problem.

I can create fix for FreeBSD, but testing it on Linux is little bit problematic.

xdt-autogen uses also hard-coded sed, but it does not cause problems.