Add dependency on twofish gem.
Add dependency on twofish gem.

Strictly, this dependency isn't required for most functionality, but
specify it for completeness so that PasswordSafe v3 functionality works
out of the box.  Require 1.0.6 or newer for the new incremental API.

Signed-off-by: brian m. carlson <738bdd359be778fee9f0fc4e2934ad72f436ceda@crustytoothpaste.net>

bk2204/daniel-ruby,bk2204/daniel-ruby