Add "IN" operator to expression parser, to evaluate membership of

a list of tokens.  Couldn't resist after sf's comment on r1002363!

This means expressions like
<If %{REQUEST_METHOD} IN GET,HEAD,OPTIONS,...>
will work as a drop-in substitute for <Limit>

Also fix off-by-one bug in variable evaluation


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1002415 13f79535-47bb-0310-9956-ffa450edef68