Create a backport branch for r1804008 (Teach the dechunk bucket to return
a proper error in presence of invalid (unparseable) chunk lengths, instead
of returning an APR_EOF).

This branch would also include related commits r1804005 and r1804016.


git-svn-id: https://svn.apache.org/repos/asf/serf/branches/1.3.x-r1804008-group@1805337 13f79535-47bb-0310-9956-ffa450edef68