DES3: Move "Two-key 3DES" support into DES.c instead of customizing tomcrypt_des.c
Pristine files from libtomcrypt-1.17

Original tarball downloaded from:

    http://libtom.org/files/crypt-1.17.tar.bz2
    http://libtom.org/files/crypt-1.17.tar.bz2.sig

SHA256 sums:

    e33b47d77a495091c8703175a25c8228aff043140b2554c08a3c3cd71f79d116 *crypt-1.17.tar.bz2
    8f52ddfb17656f7a2e510d92a26c8b33e0c1f431af7febd9cf1298a77b5fd932 *crypt-1.17.tar.bz2.sig

libtomcrypt-1.17/LICENSE says:

    LibTomCrypt is public domain.  As should all quality software be.

    Tom St Denis
PyCrypto customizations: Declare things static so that we don't leak symbols
Upgrade libtomcrypt 1.16 -> 1.17 (LP#1264130)

This should fix a FreeBSD build issue:
https://bugs.launchpad.net/pycrypto/+bug/1264130

Thanks to Richard Mitchell <richard.j.mitchell@gmail.com> for suggesting
how to fix this.
Get rid of catch-all exceptions. LP#1178485.
Fix tobytes() broken by previous commit.

Python 2.1 str objects don't have a .decode() method.
Add support for tox
tox.ini: We don't support pypy; tox no longer supports Python 2.5; add comment