Implement a length argument on input filters. There are three possible

Implement a length argument on input filters.  There are three possible
values for the length, -1, 0, and a positive number.  -1 means that the
next filter should return all the data it has, the current filter will
take care to ensure that the protocol is followed.  Most filters will
never use this, because it implies they are implementing a conn_based
input filter.  0 means give me exactly one line of data.  A positive
number means give me a maximum of n bytes.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@86567 13f79535-47bb-0310-9956-ffa450edef68