License wording issues in some files

[valholl]

Some files in the library are released under the GNU GPL; most of those use the classical template from the GPL itself and declare themselves to be under GPLv2 (no later version), but a few use the wording::

// This code is distributed under the GNU Public License
//              which can be found at http://www.gnu.org/licenses/gpl.txt

and that link currently points to version 3 of the GPL, which is not compatible with version 2.

I suspect that it is just a problem with changed contents in the link, but right now this means that the whole library can't be redistributed until the original author(s) clarify/fix it.

[valholl]

I've checked a bit more in depth, and the files that use the URL should be just avrlibdefs.h, global.h and avrlibtypes.h, and, at least in git, they were all edited just in commit 5191a3c by asynclabs (29 May 2009).