Revamp the apapi_vformatter interface to reduce copies. In this interface

the callers hand apapi_vformatter pointers into their own private buffers,
and are called back for flushing when appropriate.  This is more efficient
and seems somewhat more clean.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@80728 13f79535-47bb-0310-9956-ffa450edef68