As of now, only LibVNCServer makes uses of these digest functions _and_
they depend on sys/uio.h, but in the future LibVNCClient will need those
as well.
[jes: moved out GnuTLS and OpenSSL support, added a dummy support, to
separate changes better, and to keep things compiling]
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>