[Ltru] Issue #59: replace RECOMMENDED language with MUSTlanguage in 2.2.1 (Apps #12a)

[Alexey Melnikov <alexey.melnikov at isode.com>]

I am not entirely happy with the resolution "wantfix" for this one, as 
this is a typical case of what can bring a DISCUSS from other IESG members.
So let me try to suggest a specific text.

OLD:
At the time this document was created, there were no examples of
this kind of subtag and future registrations of this type are
discouraged: primary languages are strongly RECOMMENDED for
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
registration with ISO 639, and proposals rejected by ISO 639/ RA-
^^^^^^^^^^^^^^^^^^^^^^^^^
JAC will be closely scrutinized by the Language Subtag Reviewer
before they are registered with IANA.

NEW:
At the time this document was created, there were no examples of
this kind of subtag and future registrations of this type are
discouraged: an attempt to register a primary language MUST be
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
made to ISO 639, and proposals rejected by ISO 639/ RA-
^^^^^^^^^^^^^^^
JAC will be closely scrutinized by the Language Subtag Reviewer
before they are registered with IANA.


I.e. the discussion about what the Language Tag Reviewer is going to do 
is not the point of this issue.