fix two bugs

[wentianxiaokai]

"1,fix the bug in cetcd.c:397,modify 'if(watcher->index){' to 'if(index){',so the modified index can increase;2,fix the bug in cetcd.c:509 in the function of cetcd_multi_watch_async,the variable 'pthread_t thread' should be imported as a parameter like 'pthread_t * thread' which is mallocd by the user,so it can be use when function cetcd_multi_watch_async ended.Nor it will core.