Fixed copyright notice.

Rev: src/nettle/aes.c:1.3
Rev: src/nettle/aes.h:1.3
Rev: src/nettle/arcfour.c:1.2
Rev: src/nettle/arcfour.h:1.2
Rev: src/nettle/blowfish.h:1.5
Rev: src/nettle/cast128.c:1.2
Rev: src/nettle/cast128.h:1.2
Rev: src/nettle/des.c:1.3
Rev: src/nettle/des.h:1.3
Rev: src/nettle/macros.h:1.3
Rev: src/nettle/md5.c:1.2
Rev: src/nettle/md5.h:1.2
Rev: src/nettle/serpent.h:1.4
Rev: src/nettle/sha1.c:1.3
Rev: src/nettle/sha1.h:1.2
Rev: src/nettle/twofish.c:1.3
Rev: src/nettle/twofish.h:1.3