Fix for the code that handles SSI tokens that span multiple

Fix for the code that handles SSI tokens that span multiple
buckets: if a brigade containing an incomplete "<!--#" token
has been set aside in ctx->ssi_tag_brigade, we need to retrieve
and output the contents of that brigade if the next bucket (in
the next brigade) doesn't actually complete the "<!--#".

As part of this commit, I've commented out the recent changes
to detect flush buckets in the brigade, due to segfaults.  (I
think the fix may be to add some checks for sentinels and EOS
when advancing to the next bucket after the flush bucket.)

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@93557 13f79535-47bb-0310-9956-ffa450edef68