Moved all typedefs for function types to nettle-types.h. Use

non-pointer types, so that the types can be used to declare functions.
Updated all users.

Rev: nettle/arcfour-meta.c:1.2
Rev: nettle/cbc.h:1.2
Rev: nettle/des-compat.c:1.2
Rev: nettle/examples/nettle-benchmark.c:1.3
Rev: nettle/examples/nettle-openssl.c:1.2
Rev: nettle/examples/rsa-encrypt.c:1.2
Rev: nettle/examples/rsa-keygen.c:1.2
Rev: nettle/nettle-internal.c:1.2
Rev: nettle/nettle-meta.h:1.2
Rev: nettle/nettle-types.h:1.2
Rev: nettle/testsuite/dsa-keygen-test.c:1.3
Rev: nettle/testsuite/rsa-encrypt-test.c:1.3
Rev: nettle/testsuite/rsa-keygen-test.c:1.3
Rev: nettle/testsuite/testutils.c:1.3