fix dss key signing
(expanded on a patch from fred gansevles)
add a demo dss key for server mode, and fix some bugs that had caused the dss
signing stuff to never work before. the demo_server is a bit more verbose
now, too. both key types (RSAKey & DSSKey) now have a function to return the
fingerprint of the key, and both versions of read_private_key_file() now raise
exceptions on failure, instead of just silently setting "valid" to false.
Robey Pointer