destroying passed brigades

[Joe Orton <jo...@redhat.com>]

Any further thoughts on this, Cliff or anyone else?  At least the
core_output_filter, the byterange filter, and the http_header filter
will all destroy the brigade which is passed to them.  Many other
filters presume that it's OK to reuse brigades which have been passed
on.

With a combination of filters which assume both ways, it is inevitable
that changing apr_brigade_destroy() to actually destroy the brigade
structure will break some set of existing filters, unfortunately.

There's also ambiguity about what to do with a passed brigade if the
next filter returns an error.

joe