Backport from trunk:

Add apr_escape_ldap() and apr_pescape_ldap(), escaping characters
as described by RFC4514 and RFC4515 respectively.


git-svn-id: https://svn.apache.org/repos/asf/apr/apr/branches/1.6.x@1589981 13f79535-47bb-0310-9956-ffa450edef68