Add the ldap function to the expression API, allowing LDAP filters and
distinguished names based on expressions to be escaped correctly to
guard against LDAP injection.

Note: this requires at least APR v1.6.0 or above for the apr_escape API.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1589986 13f79535-47bb-0310-9956-ffa450edef68