Increase IOV_MAX to 50 on Windows: there is no limit for iovec count on  Windows, but apr_socket_sendv allocates internal WSABUF structures on stack  if vecs_count <= 50.
Increase IOV_MAX to 50 on Windows: there is no limit for iovec count on 
Windows, but apr_socket_sendv allocates internal WSABUF structures on stack 
if vecs_count <= 50.

* serf_private.h
  (IOV_MAX): Change to 50.

jandre/serf,jandre/serf,jandre/serf,jandre/serf