Move to LGPL3

[ryan lortie <desrt desrt ca>]

Hello.

After some talk at the Hackfest about it, I'm writing the list to
officially request that glib and GTK be moved to LGPL "version 3 or
later".

The reasons for this are the increased clarity in the language of the
license plus the ability to accept LGPL3 code into glib/gtk ((since it
seems like things will be increasingly using LGPL3 in the future)).

There is also the matter of the additional protections offered by the
LGPL3.  Everyone I talked to at the hackfest was in favour of these.

There is the option of simply making a policy change and saying "we now
accept code under LGPL3+, but existing code is still LGPL2+" and leaving
all of the copyright notices alone.  Tim thought that probably it would
be a better idea to change all of the headers to explicitly state LGPL3+
(in order to, among other things, avoid confusion about what license new
contributions occur under).

If we decide to change all of the existing copyright notices, I'd
volunteer to make the patch to do so.

Cheers