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/urldata.h

@@ -951,7 +951,7 @@ struct conncache {
   /* 'connects' will be an allocated array with pointers. If the pointer is
      set, it holds an allocated connection. */
   struct connectdata **connects;
-  long num;           /* size of the 'connects' array */
+  long num;           /* number of entries of the 'connects' array */
   enum {
     CONNCACHE_PRIVATE, /* used for an easy handle alone */
     CONNCACHE_MULTI    /* shared within a multi handle */