Do a final userscript command read on cleanup

On OS X, sometimes the userscript exited before the QSocketNotifier was
triggered. By doing a final read when cleaning up we make sure we don't
miss anything.

Fixes #1533.

qutebrowser/commands/userscripts.py

@@ -71,6 +71,8 @@ class _QtFIFOReader(QObject):
     def cleanup(self):
         """Clean up so the FIFO can be closed."""
         self._notifier.setEnabled(False)
+        for line in self._fifo:
+            self.got_line.emit(line.rstrip('\r\n'))
         self._fifo.close()
 
 

tests/end2end/features/spawn.feature

@@ -30,7 +30,7 @@ Feature: :spawn
         And I run :spawn echo {url:pretty}
         Then "Executing echo with args ['http://localhost:(port)/data/title with spaces.html'], userscript=False" should be logged
 
-    @linux
+    @posix
     Scenario: Running :spawn with userscript
         When I open about:blank
         And I execute the userscript open_current_url