The parser for fileserver.conf does not have a case allowing a single-word hostname to be used like it does for fully-qualified domain names, wildcards, and IP addresses.
Example of an "invalid" fileserver.conf:
[files]
path /to/files
allow foo
The FQDN regex won't allow this because it requires a period (".") to match.
There are probably arguments against allowing someone to put a single-word hostname in the fileserver.conf, but many simpler configurations will encounter this.
My patch (to be attached) does *not* allow wildcard matching on a single hostname. My reasoning for this decision is based on security: whereas an accidental asterisk ("*") in a FQDN may cause unintentional access rights to be granted/denied, such an error in a single-word hostname could have tremendously worse effects.
Additionally, I have changed the two nearby regexes which would not match on some allowed (and used, in my case) domains which start with numbers (00hostname.invalid). Additionally, I modified the rest of the regex to comply with the stanard "starting and ending in alphanumerics without dashes" description of the hostname/DNS RFCs.
