No trailing slash for ProxyPass/ProxyPassReverse

Remove implicitly added slashes in ProxyPassReverse location paths.
Trailing slashes should either be present on both path and url, or
absent on both. Mixing one with the other is bad. Should fix issue #511.
Merge pull request #512 from antaflos/no_trailing_slash_proxypass

No trailing slash for ProxyPass/ProxyPassReverse