scripts: xorg-release: handle case when version needs downgrade

the initial implementation assumes that when a version found in
buildroot is different from the one in the X11 release, it
requires an upgrade. even though this is most likely the case, it
could be a downgrade too, and it's probably worth highlighting
such cases when it (rarely) happens.

LooseVersion from distutils is doing the low level job of sorting
version numbers represented in strings...

[Thomas & Thomas:

  - do not count packages more recent in Buildroot than in the latest
    X.org release as to be downgraded. If we have more recent version,
    it's generally for a good reason, so we want to keep them as
    is. Such packages are counted as "nothing to do", but for
    information, we indicate that there are "More recent"

  - also remove the "nothing to do" action indicator. It used to be a
    simple dash, which was not really useful.
]

Signed-off-by: Nicolas Dechesne <ndec13@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>