#4 backward version compatible

[Duncan Ferguson]

From Yair Lenga to Magnicomp

Ability to communicate with different versions. We are
using multiple versions of Solaris and IRIX machine,
each of them
arrived with different rdist pre-installed (6.1.0 vs.
6.1.3). We had to compile and install the same version
of rdist on all platforms. It will be nice if there was
a way for rdist to detect a mismatch, and to
automatically downgrade to protocol (even at the cost
of some inefficiency).