Don't save narrow operators to the URL fragment if that's where they came from

In Firefox, prevents e.g. a slash in a stream name, which we wanted to store as
%2F, from converting back to a literal slash.

There is some appeal to normalizing the URL fragment after parsing, but in
general this way seems better.  It may decrease page load time on narrowed
views.

Doesn't yet fix #826; the URL is correct but the narrow is still wrong.

(imported from commit 32e3fa9e968139863f34b9698f1c8b39d06f0c14)

zephyr/static/js/hashchange.js

@@ -45,7 +45,10 @@ function parse_narrow(hash) {
     } else {
         new_selection = initial_pointer;
     }
-    narrow.activate(operators, {then_select_id: new_selection});
+    narrow.activate(operators, {
+        then_select_id: new_selection,
+        change_hash:    false  // already set
+    });
 }
 
 // Returns true if this function performed a narrow