In find_string(), handle eos and end-of-pipe conditions.

In get_tag(), add an XXX comment pointing out a discrepancy in the
behavior pre- and post-bucketization.

In include_cmd(), don't destroy a brigade just handed off to the next
filter.  Subsequent filters will take care of that soon enough.

Fix some compile warnings (mostly removing unused variables).


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@86228 13f79535-47bb-0310-9956-ffa450edef68