move libevent into base

base/third_party/libevent/buffer.c

 /*
  * Copyright (c) 2002, 2003 Niels Provos <provos@citi.umich.edu>
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 534 matching lines @@
         return (NULL);
 }
 
 void evbuffer_setcb(struct evbuffer *buffer,
     void (*cb)(struct evbuffer *, size_t, size_t, void *),
     void *cbarg)
 {
         buffer->cb = cb;
         buffer->cbarg = cbarg;
 }