- We support domain/forest function levels >= (Windows) 2003 Native -> adapt the
  domain/forest and DC function level restrictions.
- Consider also the lowest function level of a DC. The domain and forest function
  levels can never be higher than it.
- Improve the error handling by printing out messages to "stderr"
- Introduce the "choice" type for choice arguments (saves us some error handling)

I removed it since on some scripts it was present, on others not - so I thought
it wouldn't be really needed. This was a bad decision (pointed out by abartlet).
So I reintroduce it on all scripts (to have consistent parameters).

The second "nTMixedDomain" attribute (under Partitions/Domain-DN) is only a
copy of the one under the directory root object. Therefore there doesn't exist
the "Windows 2000 Mixed" forest level.

- The tool displays now also mixed/interim domain levels and warns about them
  (s4 isn't capable to run on them)
- But it allows now also to raise/step-up from them
- It displays now also levels higher than 2008 R2 (altough we don't support them
  yet) but to be able to get a correct output

- I removed also the "-H" parameter since those scripts are all thought for the
  use on a local s4 domain controller. Another reason is also the bind as SYSTEM
  account which itself is only possible on local binds.

This simple script allows raising the domain and/or forest level for s4.
I integrated also the basic checks (since we don't perform them in LDB yet):
e.g. the forest level can't be higher than the domain level(s).