Reported in #1561470 (http://curl.haxx.se/bug/view.cgi?id=1561470), libcurl

would crash if a bad function sequence was used when shutting down after
using the multi interface (i.e using easy_cleanup after multi_cleanup) so
precautions have been added to make sure it doesn't any more - test case 529
was added to verify.

lib/multiif.h

@@ -32,9 +32,6 @@ void Curl_multi_rmeasy(void *multi, CURL *data);
 
 bool Curl_multi_canPipeline(struct Curl_multi* multi);
 
-void Curl_multi_add_closure(struct Curl_multi *multi,
-                            struct SessionHandle *data);
-
 /* the write bits start at bit 16 for the *getsock() bitmap */
 #define GETSOCK_WRITEBITSTART 16