In libsvn_ra_serf: Keep serf connections operational when returning an error
from the xml parser and other body handlers by not returning error codes that
make serf mark the connection as failed.

This patch makes it possible to re-use the ra session after returning an
error from a log callback.

* subversion/libsvn_ra_serf/util.c
  (handle_response): Handle http status values <= 199 like other errors. We
    never expect to see these, and they should be handled by serf if we
    ever add support for them.
  (svn_ra_serf__error_on_status): Handle less common redirect status codes
    with a redirect message and status codes <= 199 as unexpected.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1553341 13f79535-47bb-0310-9956-ffa450edef68