Allow the core input filter to handle AP_NONBLOCK_READ request for a

Allow the core input filter to handle AP_NONBLOCK_READ request for a
finite number of bytes (i.e. *readbytes > 0).

ap_brigade_partition does a blocking read.  So, what we should do is
apr_bucket_read on the socket for non-blocking.  If we get less than
what they asked for, that's okay and we should just return that amount.
If they were non-blocking, we should always be non-blocking.

Ryan, Greg, and others can figure out if ap_brigade_partition should
be tweaked to handle AP_NONBLOCK_READ natively.  I'm of a mixed mind,
but this addresses the short term need.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@91312 13f79535-47bb-0310-9956-ffa450edef68