SpawnProcess._unregister: cancel PipeLogger (bug 658806)

If the PipeLogger has not closed itself before the _unregister
method has been called, then it must be cancelled so that it
will close the log immediately. This fixes the case reported
in bug 658806, where an unclosed PipeLogger instance left the
log file with a temporarily incomplete gzip stream.

Bug: https://bugs.gentoo.org/658806

pym/_emerge/SpawnProcess.py

@@ -176,6 +176,9 @@ def _unregister(self):
 		if self.cgroup is not None:
 			self._cgroup_cleanup()
 			self.cgroup = None
+		if self._pipe_logger is not None:
+			self._pipe_logger.cancel()
+			self._pipe_logger = None
 
 	def _cancel(self):
 		SubProcess._cancel(self)