Resize the connection cache upwards when adding more handles than what

currently fits in the cache, to make the cache work better especially for
pipelining cases but also for "mere" (persistent) connection re-use.

lib/url.h

@@ -50,6 +50,10 @@ void Curl_safefree(void *ptr);
 struct conncache *Curl_mk_connc(int type);
 /* free a connection cache */
 void Curl_rm_connc(struct conncache *c);
+/* Change number of entries of a connection cache */
+CURLcode Curl_ch_connc(struct SessionHandle *data,
+                       struct conncache *c,
+                       long newamount);
 
 int Curl_protocol_getsock(struct connectdata *conn,
                           curl_socket_t *socks,