update 2012 copyrights to 2013

* add 2013 where there was only 2012

Notable omissions from updates:

* contrib/bitcoind.bash-completion -- no copyright by The Bitcoin developers
* contrib/testgen/gen_base58_test_vectors.py -- no copyright by The Bitcoin developers
* src/addrman.cpp -- no copyright by The Bitcoin developers
* src/addrman.h -- no copyright by The Bitcoin developers
* src/leveldb/* -- I figure this can be updated by pulling in upstream code

Fixes #2217.