Fix #782454 (Calibre fails to compile with png-1.5)

recipes/economist.recipe

@@ -20,7 +20,7 @@ class Economist(BasicNewsRecipe):
     INDEX = 'http://www.economist.com/printedition'
     description = ('Global news and current affairs from a European'
             ' perspective. Best downloaded on Friday mornings (GMT)')
-
+    extra_css      = '.headline {font-size: x-large;} \n h2 { font-size: small;  } \n h1 { font-size: medium;  }'
     oldest_article = 7.0
     cover_url = 'http://www.economist.com/images/covers/currentcoverus_large.jpg'
     remove_tags = [

src/calibre/ebooks/pdf/images.cpp

@@ -13,6 +13,7 @@
 #include <math.h>
 #include <iostream>
 #include <wand/MagickWand.h>
+#include <zlib.h>
 
 #include "images.h"
 #include "utils.h"