Modify the content-length filter to change the criteria used to determine

Modify the content-length filter to change the criteria used to determine
if/when we compute the content-length.  There are just a few cases now:

        1) We already have all the data
        2) We don't have all the data and:
                2a)  This is a 1.1 request but we can't chunk
                2b)  The is a keep-alive request
	    In the future, we probably want to modify this to not
	    be a keep-alive request.

This filter always buffers 9K of data.  The reason is simple, the core will
buffer 9K at a time anyway, and there is a chance that we may get the end
of the request before we hit 9K.  This increases our chances of being able
to send a c-l.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@87055 13f79535-47bb-0310-9956-ffa450edef68