Allow for proxy servlet mapping at pre_translate_name stage.

Allow for proxy servlet mapping at pre_translate_name stage.

Provide alias_match_servlet(), the servlet counterpart of alias_match(),
which maps the request URI-path to the ProxyPass alias ignoring path
parameters, while still forwarding them (above the alias).

This is needed to proxy servlet URIs for application handled by Tomcat,
which can then make use of the path/segments parameters.

Github: closes #128

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1879080 13f79535-47bb-0310-9956-ffa450edef68