Log Message:
Update p5-Plack-App-Proxy to 0.19.

Changes from previous:
0.19
        - Add pluggable backends, since AnyEvent seems to be flaky on
          some systems. (doy)

0.18    02/17/2010
        - Fixes for RewriteLocation when used on a mounted proxy
          (hiratara, rbuels)
        - Ignore $ENV{http_proxy}
        - Include reason for failure in 502 response
        - Disabled persistent HTTP connection option in AnyEvent::HTTP

0.17    01/19/2010
        - Bump version to fix some CPAN issues

0.16    01/12/2010
        - Rewrite proxy code to use AnyEvent::HTTP's on_body callback.
          This gets chunked and gzipped responses working.