[libvoikko] Proposed licensing changes for libvoikko and libreoffice-voikko

["Harri Pitkänen"]

I'm planning a few licensing changes that would affect libreoffice-voikko
and parts of libvoikko:

 * Libreoffice-voikko would be licensed under GPLv3+/LGPLv3+/MPLv1.1+
   tri-license.
 * Core code of libvoikko (this includes just the parts that cannot be
   configured away, that is, backends are not affected) would be licensed
   under GPLv2+/LGPLv2+/MPLv1.1+ tri-license.

Reason for this proposal is to achieve two-way license compatibility
between LibreOffice <-> libreoffice-voikko, and Hunspell <-> core of
libvoikko. (Actually LibreOffice is currently not entirely under this
tri-license but it is their policy for all new code.)

In the immediate future nothing would change for binary code users since
the Malaga backend of libvoikko would still remain under GPLv2+. But it
will make it easier for us to integrate with LibreOffice, Firefox and
other products that currently use Hunspell for spell checking. The same
GPL/LGPL/MPL combination, with just version differences, is used across
most of the free software spell checking stack and almost all free desktop
software projects consider it acceptable to link against libraries under
this license combination.

I don't mean to suggest that more restrictively licensed backends would
become deprecated. It would still be OK to continue developing existing
and new backends and optionally depend on libraries with other licenses as
long as they are compatible with the minimal requirement of this project
(GPLv3+). Same goes for vocabulary data developed here or elsewhere,
nothing would (and nothing should in my opinion) change there either.

If you have any comments on this move, please share them within the next
month. I'm not yet entirely sure on all details myself and might have
missed something important. Thus I will wait for at least one month before
actually changing the license headers.

The code affected by this change is almost entirely written by me or is
taken from an even more liberal source. There are however some patches
that have came from other people. Most (all?) of the authors are on this
list. I'd like to ask that all such contributors state here if they are OK
with their code being relicensed. If we continue with the change, I will
contact you individually in case I don't hear from you.

Harri