Ignore "Frame load interrupted by policy change"

Searching for that error doesn't turn up many helpful results, but it
seems to be harmless and shown when downloading a file - it's also new
in Qt 5.6 it seems, so let's just ignore it.

CHANGELOG.asciidoc

@@ -74,6 +74,8 @@ Fixed
   `remove-finished-downloads` setting.
 - Fixed crash when hitting `<Tab>` then `<Ctrl-C>` on pages without keyboard
   focus.
+- Fixed "Frame load interrupted by policy change" error showing up when
+  downloading files with Qt 5.6.
 
 Removed
 ~~~~~~~

qutebrowser/browser/webpage.py

@@ -122,7 +122,10 @@ class BrowserPage(QWebPage):
         """
         ignored_errors = [
             (QWebPage.QtNetwork, QNetworkReply.OperationCanceledError),
-            (QWebPage.WebKit, 203),  # "Loading is handled by the media engine"
+            # "Loading is handled by the media engine"
+            (QWebPage.WebKit, 203),
+            # "Frame load interrupted by policy change"
+            (QWebPage.WebKit, 102),
         ]
         errpage.baseUrl = info.url
         urlstr = info.url.toDisplayString()