COPYING: Update license preamble

Update the comment about "a modification is currently under discussion"
since there hasn't been any such discussion for some time and this is
the consensus agreed upon preferred format.

Also throw in a pointer to the OSI discussion page about the MIT license.

Signed-off-by: Alan Coopersmith <alan.coopersmith@sun.com>
Signed-off-by: Daniel Stone <daniel@fooishbar.org>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>