Add sitemap.size.max

Overrides http.content.limit and file.content.limit when fetching sitemaps (which can be pretty big).
diff --git a/conf/nutch-default.xml b/conf/nutch-default.xml
index 2ba04d2..97fcbe4 100644
--- a/conf/nutch-default.xml
+++ b/conf/nutch-default.xml
@@ -2671,4 +2671,12 @@
     Maximum number of redirects to follow.
    </description>
 </property>
+
+<property>
+  <name>sitemap.size.max</name>
+  <value>52428800</value>
+  <description>
+    Maximum sitemap size in bytes.
+   </description>
+</property>
 </configuration>