Mention maxcalls support

Now that the explicit variable has gone, add a mention of how to
use call_numbers<> to determine the maximum number of calls per
connection supported by this client.

Change-Id: I46955a6465d911f894d0ae38979c0b9bed5bc430
RXGK challenges do not contain a version stamp

Such a thing would be useless without discriminated unions, which
we don't have yet.

Change-Id: I5d06b3dd80a898701765f755fafa67ca97e1cd27
Attempt to make the GSS negotiation loop correct

Describing these things is always challenging.

Change-Id: I15ac1d7c8962aac6cd853cbcc404c55df52a8a04
Talk about acceptor principal names for GSSNegotiate

The client has to know the target principal's name; give it a
suggestion for when it knows better.
The server, however, should not specify a name, since that would
be overly restrictive.

Change-Id: I24481178aef93b40ae10097f9b76e3765431bbb0