patch 8.1.1439: json_encode() is very slow for large results

Problem:    Json_encode() is very slow for large results.
Solution:   In the growarray use a growth of at least 50%. (Ken Takata,
            closes #4461)

src/misc2.c

@@ -2057,6 +2057,13 @@ ga_grow(garray_T *gap, int n)
     {
 	if (n < gap->ga_growsize)
 	    n = gap->ga_growsize;
+
+	// A linear growth is very inefficient when the array grows big.  This
+	// is a compromise between allocating memory that won't be used and too
+	// many copy operations. A factor of 1.5 seems reasonable.
+	if (n < gap->ga_len / 2)
+	    n = gap->ga_len / 2;
+
 	new_len = gap->ga_itemsize * (gap->ga_len + n);
 	pp = vim_realloc(gap->ga_data, new_len);
 	if (pp == NULL)

src/version.c

@@ -767,6 +767,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1439,
 /**/
     1438,
 /**/