Switch ftp_directory_charset and interpolate_env in proxy_dir_conf,

with a major MMN bump.  As suggested by rpluem in r661069 to enable
backport *without* a major bump (ABI breakage) in 2.2.x.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@661079 13f79535-47bb-0310-9956-ffa450edef68