Relax the checking of Host: headers so that only character sequences that

are sensitive to the filesystem are rejected, i.e. forward slashes,
backward slashes, and sequences of more than one dot. This supports iDNS
without compromising the safety of mass vhosting.

PR: 6635


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@87803 13f79535-47bb-0310-9956-ffa450edef68