Validate SP path settings during installation
    
    There are a number of URL path options that can be specified as
    options when running ipsilon-client-install. There are certain
    rules that must be followed to result in a valid mod_auth_mellon
    configuration:
    
     - All path options must be prefixed with '/'.
    
     - The mellon endpoint path (--saml-sp) must be a subpath of the
       httpd 'Location' element is it contained within (--saml-base).
    
     - The logout (--saml-sp-logout) and post (--saml-sp-post) paths
       must be subpaths of the mellon endpoint (--saml-sp).
    
    This adds validation for all of the above rules.
    
    https://fedorahosted.org/ipsilon/ticket/82
    
    Signed-off-by: Nathan Kinder <nkinder@redhat.com>
    Reviewed-by: Patrick Uiterwijk <puiterwijk@redhat.com>