#7 Allow to build against OpenSSl without MD4 support

[Alexey Dokuchaev]

While RIPEMD160 and WHIRLPOOL support in RHash is optional, MD4 for some reason is not. Some users prefer to build their OpenSSL without MD4 which is considered unsafe, and then RHash fails to build against it. Consider attached patch which makes it optional as well.

[Aleksey]

Thanks for the patch!

Applied as 551e07233.