rsbackup should allow all valid DNS hostnames as host names

[pm215]

I have a machine I'm backing up whose hostname happens to contain hyphens ("cam-vm-266"). I did the obvious thing and used the hostname as the 'HOST' part of the host stanza:
root@e104462:~# cat /etc/rsbackup/hosts.d/cam-vm-266
host cam-vm-266
hostname cam-vm-266.mydomain.com
volume root /
exclude /tmp/*
exclude /var/lib/schroot/mount/*

and rsbackup complains:
root@e104462:~# rsbackup --backup --dry-run
ERROR: /etc/rsbackup/hosts.d/cam-vm-266:1: invalid host name

Removing all the 'hyphens' from the "host" line placates it, but it would be nice if the allowed character sets lined up.

[ewxrjk]

Historically the reason for '-' being prohibited was the parsing of logfile names, which used that character as a separator.
In the next release these logfiles mostly don't exist. The one place they do exist is during upgrade from previous versions! But since previous versions can't have names with dashes in it shouldn't be possible to cause an ambiguous parse.
So I think this restriction can be loosened without risk in the next release.