rsaenh/tests: Add DES/3DES-112 const buffer test

[Marvin]

Hi,

While running your changed tests on Windows, I think I found new failures.
Being a bot and all I'm not very good at pattern recognition, so I might be
wrong, but could you please double-check?
Full results can be found at
https://testbot.winehq.org/JobDetails.pl?Key=7931

Your paranoid android.


=== w2000pro (32 bit rsaenh) ===
rsaenh.c:905: Test failed: DES encryption failed!