Update to COPYING.LIB to latest LGPLv2.1 copy
    
    The text version
    of LGPLv2.1 available at
    http://www.gnu.org/licenses/old-licenses/lgpl-2.1.txt is slightly
    different from COPYING.LIB:
    - several paragraphs were rewrapped
    - the FSF address has changed, so the license has been changed to
      indicate the newer address
    
    I've checked that there are no changes in the license text apart from
    the updated address, which is what I want to fix with this commit.