Update COPYING with GPLv2 with new FSF address

The mailing address of FSF changed quite a while ago.  Also the expansion
of the acronym LGPL (which we don't use) is "Lesser GPL" not "Library GPL"
these days in recent copies of GPLv2.  Update the copy we have with a
fresh download of <http://www.gnu.org/licenses/gpl-2.0.txt

>.

This incidentally removes form-feeds in the text we retained for all these
years.

Signed-off-by: Junio C Hamano <gitster@pobox.com>